[for-next][PATCH 00/18] tracing: Updatse for 5.9

[for-next][PATCH 00/18] tracing: Updatse for 5.9

[Steven Rostedt]

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
for-next

Head SHA1: 29ce24519c0692ca7d998d7444a9e016a4c44fa7


Nicholas Piggin (1):
      ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU

Steven Rostedt (VMware) (13):
      tracing: Only allow trace_array_printk() to be used by instances
      x86/ftrace: Make non direct case the default in ftrace_regs_caller
      x86/ftrace: Only have the builtin ftrace_regs_caller call direct hooks
      x86/ftrace: Do not jump to direct code in created trampolines
      tracing: Move pipe reference to trace array instead of current_tracer
      ring-buffer: Have nested events still record running time stamp
      ring-buffer: Incorporate absolute timestamp into add_timestamp logic
      ring-buffer: Add rb_time_t 64 bit operations for speeding up 32 bit
      ring-buffer: Mark the !tail (crossing a page) as unlikely
      ring-buffer: Consolidate add_timestamp to remove some branches
      ring-buffer: Move the add_timestamp into its own function
      ring-buffer: Call trace_clock_local() directly for RETPOLINE kernels
      ring-buffer: Do not trigger a WARN if clock going backwards is detected

Wei Yang (4):
      tracing: not necessary to undefine DEFINE_EVENT again
      tracing: not necessary re-define DEFINE_EVENT_PRINT
      tracing: define DEFINE_EVENT_PRINT not related to DEFINE_EVENT
      tracing: not necessary to define DEFINE_EVENT_PRINT to be empty again

----
 arch/x86/kernel/ftrace.c     |  14 +-
 arch/x86/kernel/ftrace_64.S  |  29 +-
 include/linux/ring_buffer.h  |   1 +
 include/trace/trace_events.h |  19 +-
 kernel/trace/ftrace.c        |   8 +
 kernel/trace/ring_buffer.c   | 694 ++++++++++++++++++++++++++++++++++---------
 kernel/trace/trace.c         |  26 +-
 kernel/trace/trace.h         |   2 +-
 8 files changed, 600 insertions(+), 193 deletions(-)

[for-next][PATCH 01/18] tracing: Only allow trace_array_printk() to be used by instances

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

To prevent default "trace_printks()" from spamming the top level tracing
ring buffer, only allow trace instances to use trace_array_printk() (which
can be used without the trace_printk() start up warning).

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index bb62269724d5..8241d1448d70 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3346,12 +3346,16 @@ int trace_array_printk(struct trace_array *tr,
 	int ret;
 	va_list ap;
 
-	if (!(global_trace.trace_flags & TRACE_ITER_PRINTK))
-		return 0;
-
 	if (!tr)
 		return -ENOENT;
 
+	/* This is only allowed for created instances */
+	if (tr == &global_trace)
+		return 0;
+
+	if (!(tr->trace_flags & TRACE_ITER_PRINTK))
+		return 0;
+
 	va_start(ap, fmt);
 	ret = trace_array_vprintk(tr, ip, fmt, ap);
 	va_end(ap);
-- 
2.26.2

[for-next][PATCH 02/18] x86/ftrace: Make non direct case the default in ftrace_regs_caller

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a direct function is hooked along with one of the ftrace registered
functions, then the ftrace_regs_caller is attached to the function that
shares the direct hook as well as the ftrace hook. The ftrace_regs_caller
will call ftrace_ops_list_func() that iterates through all the registered
ftrace callbacks, and if there's a direct callback attached to that
function, the direct ftrace_ops callback is called to notify that
ftrace_regs_caller to return to the direct caller instead of going back to
the function that called it.

But this is a very uncommon case. Currently, the code has it as the default
case. Modify ftrace_regs_caller to make the default case (the non jump) to
just return normally, and have the jump to the handling of the direct
caller.

Link: http://lkml.kernel.org/r/20200422162750.350373278@goodmis.org

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/x86/kernel/ftrace_64.S | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 083a3da7bb73..3ba32cc58f01 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -241,22 +241,9 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
 	 */
 	movq ORIG_RAX(%rsp), %rax
 	testq	%rax, %rax
-	jz	1f
+	jnz	1f
 
-	/* Swap the flags with orig_rax */
-	movq MCOUNT_REG_SIZE(%rsp), %rdi
-	movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
-	movq %rax, MCOUNT_REG_SIZE(%rsp)
-
-	restore_mcount_regs 8
-	/* Restore flags */
-	popfq
-
-SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL);
-	UNWIND_HINT_RET_OFFSET
-	jmp	ftrace_epilogue
-
-1:	restore_mcount_regs
+	restore_mcount_regs
 	/* Restore flags */
 	popfq
 
@@ -266,9 +253,21 @@ SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL);
 	 * The trampoline will add the code to jump
 	 * to the return.
 	 */
-SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
+SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL)
 	jmp ftrace_epilogue
 
+	/* Swap the flags with orig_rax */
+1:	movq MCOUNT_REG_SIZE(%rsp), %rdi
+	movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
+	movq %rax, MCOUNT_REG_SIZE(%rsp)
+
+	restore_mcount_regs 8
+	/* Restore flags */
+	popfq
+SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
+	UNWIND_HINT_RET_OFFSET
+	jmp	ftrace_epilogue
+
 SYM_FUNC_END(ftrace_regs_caller)
 
 
-- 
2.26.2

[for-next][PATCH 03/18] x86/ftrace: Only have the builtin ftrace_regs_caller call direct hooks

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a direct hook is attached to a function that ftrace also has a function
attached to it, then it is required that the ftrace_ops_list_func() is used
to iterate over the registered ftrace callbacks. This will also include the
direct ftrace_ops helper, that tells ftrace_regs_caller where to return to
(the direct callback and not the function that called it).

As this direct helper is only to handle the case of ftrace callbacks
attached to the same function as the direct callback, the ftrace callback
allocated trampolines (used to only call them), should never be used to
return back to a direct callback.

Only copy the portion of the ftrace_regs_caller that will return back to
what called it, and not the portion that returns back to the direct caller.

The direct ftrace_ops must then pick the ftrace_regs_caller builtin function
as its own trampoline to ensure that it will never have one allocated for
it (which would not include the handling of direct callbacks).

Link: http://lkml.kernel.org/r/20200422162750.495903799@goodmis.org

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/x86/kernel/ftrace.c    | 7 -------
 arch/x86/kernel/ftrace_64.S | 3 +--
 kernel/trace/ftrace.c       | 8 ++++++++
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 51504566b3a6..d1a0190fef5b 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -367,13 +367,6 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	if (WARN_ON(ret < 0))
 		goto fail;
 
-	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
-		ip = trampoline + (ftrace_regs_caller_ret - ftrace_regs_caller);
-		ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
-		if (WARN_ON(ret < 0))
-			goto fail;
-	}
-
 	/*
 	 * The address of the ftrace_ops that is used for this trampoline
 	 * is stored at the end of the trampoline. This will be used to
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 3ba32cc58f01..43cf9a2b52c7 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -253,7 +253,7 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
 	 * The trampoline will add the code to jump
 	 * to the return.
 	 */
-SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL)
+SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
 	jmp ftrace_epilogue
 
 	/* Swap the flags with orig_rax */
@@ -264,7 +264,6 @@ SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL)
 	restore_mcount_regs 8
 	/* Restore flags */
 	popfq
-SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
 	UNWIND_HINT_RET_OFFSET
 	jmp	ftrace_epilogue
 
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 1903b80db6eb..c141d347f71a 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2388,6 +2388,14 @@ struct ftrace_ops direct_ops = {
 	.flags		= FTRACE_OPS_FL_IPMODIFY | FTRACE_OPS_FL_RECURSION_SAFE
 			  | FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS
 			  | FTRACE_OPS_FL_PERMANENT,
+	/*
+	 * By declaring the main trampoline as this trampoline
+	 * it will never have one allocated for it. Allocated
+	 * trampolines should not call direct functions.
+	 * The direct_ops should only be called by the builtin
+	 * ftrace_regs_caller trampoline.
+	 */
+	.trampoline	= FTRACE_REGS_ADDR,
 };
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
-- 
2.26.2

[for-next][PATCH 04/18] x86/ftrace: Do not jump to direct code in created trampolines

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

When creating a trampoline based on the ftrace_regs_caller code, nop out the
jnz test that would jmup to the code that would return to a direct caller
(stored in the ORIG_RAX field) and not back to the function that called it.

Link: http://lkml.kernel.org/r/20200422162750.638839749@goodmis.org

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/x86/kernel/ftrace.c    | 15 +++++++++++++++
 arch/x86/kernel/ftrace_64.S |  1 +
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index d1a0190fef5b..7edbd5ee5ed4 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -286,6 +286,7 @@ extern void ftrace_regs_caller_ret(void);
 extern void ftrace_caller_end(void);
 extern void ftrace_caller_op_ptr(void);
 extern void ftrace_regs_caller_op_ptr(void);
+extern void ftrace_regs_caller_jmp(void);
 
 /* movq function_trace_op(%rip), %rdx */
 /* 0x48 0x8b 0x15 <offset-to-ftrace_trace_op (4 bytes)> */
@@ -316,6 +317,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	unsigned long end_offset;
 	unsigned long op_offset;
 	unsigned long call_offset;
+	unsigned long jmp_offset;
 	unsigned long offset;
 	unsigned long npages;
 	unsigned long size;
@@ -333,11 +335,13 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 		end_offset = (unsigned long)ftrace_regs_caller_end;
 		op_offset = (unsigned long)ftrace_regs_caller_op_ptr;
 		call_offset = (unsigned long)ftrace_regs_call;
+		jmp_offset = (unsigned long)ftrace_regs_caller_jmp;
 	} else {
 		start_offset = (unsigned long)ftrace_caller;
 		end_offset = (unsigned long)ftrace_caller_end;
 		op_offset = (unsigned long)ftrace_caller_op_ptr;
 		call_offset = (unsigned long)ftrace_call;
+		jmp_offset = 0;
 	}
 
 	size = end_offset - start_offset;
@@ -367,6 +371,17 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
 	if (WARN_ON(ret < 0))
 		goto fail;
 
+	/* No need to test direct calls on created trampolines */
+	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
+		/* NOP the jnz 1f; but make sure it's a 2 byte jnz */
+		ip = trampoline + (jmp_offset - start_offset);
+		if (WARN_ON(*(char *)ip != 0x75))
+			goto fail;
+		ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);
+		if (ret < 0)
+			goto fail;
+	}
+
 	/*
 	 * The address of the ftrace_ops that is used for this trampoline
 	 * is stored at the end of the trampoline. This will be used to
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 43cf9a2b52c7..ac3d5f22fe64 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -241,6 +241,7 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
 	 */
 	movq ORIG_RAX(%rsp), %rax
 	testq	%rax, %rax
+SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL)
 	jnz	1f
 
 	restore_mcount_regs
-- 
2.26.2

Re: [for-next][PATCH 04/18] x86/ftrace: Do not jump to direct code in created trampolines

[Peter Zijlstra]

On Thu, Jul 02, 2020 at 05:58:16PM -0400, Steven Rostedt wrote:

> +	/* No need to test direct calls on created trampolines */
> +	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
> +		/* NOP the jnz 1f; but make sure it's a 2 byte jnz */
> +		ip = trampoline + (jmp_offset - start_offset);
> +		if (WARN_ON(*(char *)ip != 0x75))
> +			goto fail;
> +		ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);

I really don't get this paranoia, what's wrong with memcpy() ?

> +		if (ret < 0)
> +			goto fail;
> +	}

How about something like this?

--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -359,17 +359,11 @@ create_trampoline(struct ftrace_ops *ops
 	npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
 
 	/* Copy ftrace_caller onto the trampoline memory */
-	ret = copy_from_kernel_nofault(trampoline, (void *)start_offset, size);
-	if (WARN_ON(ret < 0))
-		goto fail;
-
-	ip = trampoline + size;
+	memcpy(trampoline, (void *)start_offset, size);
 
 	/* The trampoline ends with ret(q) */
-	retq = (unsigned long)ftrace_stub;
-	ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
-	if (WARN_ON(ret < 0))
-		goto fail;
+	ip = trampoline + size;
+	memcpy(ip, text_gen_insn(RET_INSN_OPCODE, NULL, NULL), RET_INSN_SIZE);
 
 	/* No need to test direct calls on created trampolines */
 	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
@@ -377,9 +371,7 @@ create_trampoline(struct ftrace_ops *ops
 		ip = trampoline + (jmp_offset - start_offset);
 		if (WARN_ON(*(char *)ip != 0x75))
 			goto fail;
-		ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);
-		if (ret < 0)
-			goto fail;
+		memcpy(ip, ideal_nops[2], 2);
 	}
 
 	/*

Re: [for-next][PATCH 04/18] x86/ftrace: Do not jump to direct code in created trampolines

[Steven Rostedt]

On Fri, 3 Jul 2020 10:10:00 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, Jul 02, 2020 at 05:58:16PM -0400, Steven Rostedt wrote:
> 
> > +	/* No need to test direct calls on created trampolines */
> > +	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
> > +		/* NOP the jnz 1f; but make sure it's a 2 byte jnz */
> > +		ip = trampoline + (jmp_offset - start_offset);
> > +		if (WARN_ON(*(char *)ip != 0x75))
> > +			goto fail;
> > +		ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);  
> 
> I really don't get this paranoia, what's wrong with memcpy() ?

Habit. As when ftrace was introduced, it was extremely careful about
touching memory like this. And even with all of that extra care, we
still broke NICs (actually, some of the reason those NICs broke was
because of the extra care we took :-p)

> 
> > +		if (ret < 0)
> > +			goto fail;
> > +	}  
> 
> How about something like this?
> 
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -359,17 +359,11 @@ create_trampoline(struct ftrace_ops *ops
>  	npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
>  
>  	/* Copy ftrace_caller onto the trampoline memory */
> -	ret = copy_from_kernel_nofault(trampoline, (void *)start_offset, size);
> -	if (WARN_ON(ret < 0))
> -		goto fail;
> -
> -	ip = trampoline + size;
> +	memcpy(trampoline, (void *)start_offset, size);
>  
>  	/* The trampoline ends with ret(q) */
> -	retq = (unsigned long)ftrace_stub;
> -	ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
> -	if (WARN_ON(ret < 0))
> -		goto fail;
> +	ip = trampoline + size;
> +	memcpy(ip, text_gen_insn(RET_INSN_OPCODE, NULL, NULL), RET_INSN_SIZE);
>  
>  	/* No need to test direct calls on created trampolines */
>  	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
> @@ -377,9 +371,7 @@ create_trampoline(struct ftrace_ops *ops
>  		ip = trampoline + (jmp_offset - start_offset);
>  		if (WARN_ON(*(char *)ip != 0x75))
>  			goto fail;
> -		ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);
> -		if (ret < 0)
> -			goto fail;
> +		memcpy(ip, ideal_nops[2], 2);

If you want to add this change on top of this, then I'm fine with that.

If it breaks something, I can at least point the blame at you ;-)

-- Steve


>  	}
>  
>  	/*

[for-next][PATCH 05/18] tracing: not necessary to undefine DEFINE_EVENT again

[Steven Rostedt]

From: Wei Yang <richard.weiyang@linux.alibaba.com>

After un-define DEFINE_EVENT in Stage 2, DEFINE_EVENT is not defined to a
specific form. It is not necessary to un-define it again.

Let's skip this.

Link: http://lkml.kernel.org/r/20200612092844.56107-2-richard.weiyang@linux.alibaba.com

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/trace/trace_events.h | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
index 502c7be50b8d..a4994761bdaf 100644
--- a/include/trace/trace_events.h
+++ b/include/trace/trace_events.h
@@ -443,9 +443,6 @@ static struct trace_event_fields trace_event_fields_##call[] = {	\
 	tstruct								\
 	{} };
 
-#undef DEFINE_EVENT
-#define DEFINE_EVENT(template, name, proto, args)
-
 #undef DEFINE_EVENT_PRINT
 #define DEFINE_EVENT_PRINT(template, name, proto, args, print)	\
 	DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
@@ -523,9 +520,6 @@ static inline notrace int trace_event_get_offsets_##call(		\
 	return __data_size;						\
 }
 
-#undef DEFINE_EVENT
-#define DEFINE_EVENT(template, name, proto, args)
-
 #undef DEFINE_EVENT_PRINT
 #define DEFINE_EVENT_PRINT(template, name, proto, args, print)	\
 	DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
-- 
2.26.2

[for-next][PATCH 06/18] tracing: not necessary re-define DEFINE_EVENT_PRINT

[Steven Rostedt]

From: Wei Yang <richard.weiyang@linux.alibaba.com>

The definition of DEFINE_EVENT_PRINT is not changed after previous one,
so not necessary to re-define is as the same form.

Link: http://lkml.kernel.org/r/20200612092844.56107-3-richard.weiyang@linux.alibaba.com

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/trace/trace_events.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
index a4994761bdaf..5219f81b9d74 100644
--- a/include/trace/trace_events.h
+++ b/include/trace/trace_events.h
@@ -520,10 +520,6 @@ static inline notrace int trace_event_get_offsets_##call(		\
 	return __data_size;						\
 }
 
-#undef DEFINE_EVENT_PRINT
-#define DEFINE_EVENT_PRINT(template, name, proto, args, print)	\
-	DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
-
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
 
 /*
-- 
2.26.2

[for-next][PATCH 07/18] tracing: define DEFINE_EVENT_PRINT not related to DEFINE_EVENT

[Steven Rostedt]

From: Wei Yang <richard.weiyang@linux.alibaba.com>

Current definition define DEFINE_EVENT_PRINT to be DEFINE_EVENT.
Actually, at this point DEFINE_EVENT is already an empty macro. Let's
cut the relationship between DEFINE_EVENT_PRINT and DEFINE_EVENT.

Link: http://lkml.kernel.org/r/20200612092844.56107-4-richard.weiyang@linux.alibaba.com

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/trace/trace_events.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
index 5219f81b9d74..43023c3e9d74 100644
--- a/include/trace/trace_events.h
+++ b/include/trace/trace_events.h
@@ -210,8 +210,7 @@ TRACE_MAKE_SYSTEM_STR();
 #define DEFINE_EVENT(template, name, proto, args)
 
 #undef DEFINE_EVENT_PRINT
-#define DEFINE_EVENT_PRINT(template, name, proto, args, print)	\
-	DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
+#define DEFINE_EVENT_PRINT(template, name, proto, args, print)
 
 #undef TRACE_EVENT_FLAGS
 #define TRACE_EVENT_FLAGS(event, flag)
@@ -444,8 +443,7 @@ static struct trace_event_fields trace_event_fields_##call[] = {	\
 	{} };
 
 #undef DEFINE_EVENT_PRINT
-#define DEFINE_EVENT_PRINT(template, name, proto, args, print)	\
-	DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
+#define DEFINE_EVENT_PRINT(template, name, proto, args, print)
 
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
 
-- 
2.26.2

[for-next][PATCH 08/18] tracing: not necessary to define DEFINE_EVENT_PRINT to be empty again

[Steven Rostedt]

From: Wei Yang <richard.weiyang@linux.alibaba.com>

After the previous cleanup, DEFINE_EVENT_PRINT's definition has no
relationship with DEFINE_EVENT. So After we re-define DEFINE_EVENT, it
is not necessary to define DEFINE_EVENT_PRINT to be empty again.

Link: http://lkml.kernel.org/r/20200612092844.56107-5-richard.weiyang@linux.alibaba.com

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/trace/trace_events.h | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
index 43023c3e9d74..1bc3e7bba9a4 100644
--- a/include/trace/trace_events.h
+++ b/include/trace/trace_events.h
@@ -709,9 +709,6 @@ static inline void ftrace_test_probe_##call(void)			\
 	check_trace_callback_type_##call(trace_event_raw_event_##template); \
 }
 
-#undef DEFINE_EVENT_PRINT
-#define DEFINE_EVENT_PRINT(template, name, proto, args, print)
-
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
 
 #undef __entry
-- 
2.26.2

[for-next][PATCH 09/18] tracing: Move pipe reference to trace array instead of current_tracer

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

If a process has the trace_pipe open on a trace_array, the current tracer
for that trace array should not be changed. This was original enforced by a
global lock, but when instances were introduced, it was moved to the
current_trace. But this structure is shared by all instances, and a
trace_pipe is for a single instance. There's no reason that a process that
has trace_pipe open on one instance should prevent another instance from
changing its current tracer. Move the reference counter to the trace_array
instead.

This is marked as "Fixes" but is more of a clean up than a true fix.
Backport if you want, but its not critical.

Fixes: cf6ab6d9143b1 ("tracing: Add ref count to tracer for when they are being read by pipe")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 12 ++++++------
 kernel/trace/trace.h |  2 +-
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8241d1448d70..64c5b8146cca 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5891,7 +5891,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 	}
 
 	/* If trace pipe files are being read, we can't change the tracer */
-	if (tr->current_trace->ref) {
+	if (tr->trace_ref) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -6107,7 +6107,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
 
 	nonseekable_open(inode, filp);
 
-	tr->current_trace->ref++;
+	tr->trace_ref++;
 out:
 	mutex_unlock(&trace_types_lock);
 	return ret;
@@ -6126,7 +6126,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
 
 	mutex_lock(&trace_types_lock);
 
-	tr->current_trace->ref--;
+	tr->trace_ref--;
 
 	if (iter->trace->pipe_close)
 		iter->trace->pipe_close(iter);
@@ -7428,7 +7428,7 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)
 
 	filp->private_data = info;
 
-	tr->current_trace->ref++;
+	tr->trace_ref++;
 
 	mutex_unlock(&trace_types_lock);
 
@@ -7529,7 +7529,7 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
 
 	mutex_lock(&trace_types_lock);
 
-	iter->tr->current_trace->ref--;
+	iter->tr->trace_ref--;
 
 	__trace_array_put(iter->tr);
 
@@ -8737,7 +8737,7 @@ static int __remove_instance(struct trace_array *tr)
 	int i;
 
 	/* Reference counter for a newly created trace array = 1. */
-	if (tr->ref > 1 || (tr->current_trace && tr->current_trace->ref))
+	if (tr->ref > 1 || (tr->current_trace && tr->trace_ref))
 		return -EBUSY;
 
 	list_del(&tr->list);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 13db4000af3f..f21607f87189 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -356,6 +356,7 @@ struct trace_array {
 	struct trace_event_file *trace_marker_file;
 	cpumask_var_t		tracing_cpumask; /* only trace on set CPUs */
 	int			ref;
+	int			trace_ref;
 #ifdef CONFIG_FUNCTION_TRACER
 	struct ftrace_ops	*ops;
 	struct trace_pid_list	__rcu *function_pids;
@@ -547,7 +548,6 @@ struct tracer {
 	struct tracer		*next;
 	struct tracer_flags	*flags;
 	int			enabled;
-	int			ref;
 	bool			print_max;
 	bool			allow_instances;
 #ifdef CONFIG_TRACER_MAX_TRACE
-- 
2.26.2

Re: [for-next][PATCH 09/18] tracing: Move pipe reference to trace array instead of current_tracer

[dann frazier]

On Thu, Jul 02, 2020 at 05:58:21PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> 
> If a process has the trace_pipe open on a trace_array, the current tracer
> for that trace array should not be changed. This was original enforced by a
> global lock, but when instances were introduced, it was moved to the
> current_trace. But this structure is shared by all instances, and a
> trace_pipe is for a single instance. There's no reason that a process that
> has trace_pipe open on one instance should prevent another instance from
> changing its current tracer. Move the reference counter to the trace_array
> instead.
> 
> This is marked as "Fixes" but is more of a clean up than a true fix.
> Backport if you want, but its not critical.

Thanks Steven! In case it helps backport consideration, I wanted to
note that this addresses an issue we've seen with users trying to
change current_tracer when they happen to have rasdaemon
installed. rasdaemon uses the trace_pipe interface at runtime, which
therefore blocks changing the current tracer. But of course, unless
you know about rasdaemon internals, it isn't exactly an obvious
failure mode.

  -dann

> Fixes: cf6ab6d9143b1 ("tracing: Add ref count to tracer for when they are being read by pipe")
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
>  kernel/trace/trace.c | 12 ++++++------
>  kernel/trace/trace.h |  2 +-
>  2 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 8241d1448d70..64c5b8146cca 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5891,7 +5891,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
>  	}
>  
>  	/* If trace pipe files are being read, we can't change the tracer */
> -	if (tr->current_trace->ref) {
> +	if (tr->trace_ref) {
>  		ret = -EBUSY;
>  		goto out;
>  	}
> @@ -6107,7 +6107,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
>  
>  	nonseekable_open(inode, filp);
>  
> -	tr->current_trace->ref++;
> +	tr->trace_ref++;
>  out:
>  	mutex_unlock(&trace_types_lock);
>  	return ret;
> @@ -6126,7 +6126,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
>  
>  	mutex_lock(&trace_types_lock);
>  
> -	tr->current_trace->ref--;
> +	tr->trace_ref--;
>  
>  	if (iter->trace->pipe_close)
>  		iter->trace->pipe_close(iter);
> @@ -7428,7 +7428,7 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)
>  
>  	filp->private_data = info;
>  
> -	tr->current_trace->ref++;
> +	tr->trace_ref++;
>  
>  	mutex_unlock(&trace_types_lock);
>  
> @@ -7529,7 +7529,7 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
>  
>  	mutex_lock(&trace_types_lock);
>  
> -	iter->tr->current_trace->ref--;
> +	iter->tr->trace_ref--;
>  
>  	__trace_array_put(iter->tr);
>  
> @@ -8737,7 +8737,7 @@ static int __remove_instance(struct trace_array *tr)
>  	int i;
>  
>  	/* Reference counter for a newly created trace array = 1. */
> -	if (tr->ref > 1 || (tr->current_trace && tr->current_trace->ref))
> +	if (tr->ref > 1 || (tr->current_trace && tr->trace_ref))
>  		return -EBUSY;
>  
>  	list_del(&tr->list);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 13db4000af3f..f21607f87189 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -356,6 +356,7 @@ struct trace_array {
>  	struct trace_event_file *trace_marker_file;
>  	cpumask_var_t		tracing_cpumask; /* only trace on set CPUs */
>  	int			ref;
> +	int			trace_ref;
>  #ifdef CONFIG_FUNCTION_TRACER
>  	struct ftrace_ops	*ops;
>  	struct trace_pid_list	__rcu *function_pids;
> @@ -547,7 +548,6 @@ struct tracer {
>  	struct tracer		*next;
>  	struct tracer_flags	*flags;
>  	int			enabled;
> -	int			ref;
>  	bool			print_max;
>  	bool			allow_instances;
>  #ifdef CONFIG_TRACER_MAX_TRACE

Re: [for-next][PATCH 09/18] tracing: Move pipe reference to trace array instead of current_tracer

[Steven Rostedt]

On Fri, 31 Jul 2020 13:33:45 -0600
dann frazier <dann.frazier@canonical.com> wrote:

> > This is marked as "Fixes" but is more of a clean up than a true fix.
> > Backport if you want, but its not critical.  
> 
> Thanks Steven! In case it helps backport consideration, I wanted to
> note that this addresses an issue we've seen with users trying to
> change current_tracer when they happen to have rasdaemon
> installed. rasdaemon uses the trace_pipe interface at runtime, which
> therefore blocks changing the current tracer. But of course, unless
> you know about rasdaemon internals, it isn't exactly an obvious
> failure mode.

Ah, then this should probably be backported.

When I push to Linus (during the next merge window) and it gets into
Linus's tree. Feel free to send stable@vger.kernel.org the sha1 of this
commit, and ask for it to be backported for the above stated reason.

-- Steve

Re: [for-next][PATCH 09/18] tracing: Move pipe reference to trace array instead of current_tracer

[dann frazier]

On Fri, Jul 31, 2020 at 3:16 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Fri, 31 Jul 2020 13:33:45 -0600
> dann frazier <dann.frazier@canonical.com> wrote:
>
> > > This is marked as "Fixes" but is more of a clean up than a true fix.
> > > Backport if you want, but its not critical.
> >
> > Thanks Steven! In case it helps backport consideration, I wanted to
> > note that this addresses an issue we've seen with users trying to
> > change current_tracer when they happen to have rasdaemon
> > installed. rasdaemon uses the trace_pipe interface at runtime, which
> > therefore blocks changing the current tracer. But of course, unless
> > you know about rasdaemon internals, it isn't exactly an obvious
> > failure mode.
>
> Ah, then this should probably be backported.
>
> When I push to Linus (during the next merge window) and it gets into
> Linus's tree. Feel free to send stable@vger.kernel.org the sha1 of this
> commit, and ask for it to be backported for the above stated reason.

Will do.

 -dann

[for-next][PATCH 10/18] ring-buffer: Have nested events still record running time stamp

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Up until now, if an event is interrupted while it is recorded by an
interrupt, and that interrupt records events, the time of those events will
all be the same. This is because events only record the delta of the time
since the previous event (or beginning of a page), and to handle updating
the time keeping for that of nested events is extremely racy. After years of
thinking about this and several failed attempts, I finally have a solution
to solve this puzzle.

The problem is that you need to atomically calculate the delta and then
update the time stamp you made the delta from, as well as then record it
into the buffer, all this while at any time an interrupt can come in and
do the same thing. This is easy to solve with heavy weight atomics, but that
would be detrimental to the performance of the ring buffer. The current
state of affairs sacrificed the time deltas for nested events for
performance.

The reason for previous failed attempts at solving this puzzle was because I
was trying to completely avoid slow atomic operations like cmpxchg. I final
came to the conclusion to always avoid cmpxchg is not possible, which is why
those previous attempts always failed. But it is possible to pick one path
(the most common case) and avoid cmpxchg in that path, which is the "fast
path". The most common case is that an event will not be interrupted and
have other events added into it. An event can detect if it has
interrupted another event, and for these cases we can make it the slow
path and use the heavy operations like cmpxchg.

One more player was added to the game that made this possible, and that is
the "absolute timestamp" (by Tom Zanussi) that allows us to inject a full 59
bit time stamp. (Of course this breaks if a machine is running for more than
18 years without a reboot!).

There's barrier() placements around for being paranoid, even when they
are not needed because of other atomic functions near by. But those
should not hurt, as if they are not needed, they basically become a nop.

Note, this also makes the race window much smaller, which means there
are less slow paths to slow down the performance.

The basic idea is that there's two main paths taken.

 1) Not being interrupted between time stamps and reserving buffer space.
    In this case, the time stamps taken are true to the location in the
    buffer.

 2) Was interrupted by another path between taking time stamps and reserving
    buffer space.

The objective is to know what the delta is from the last reserved location
in the buffer.

As it is possible to detect if an event is interrupting another event before
reserving data, space is added to the length to be reserved to inject a full
time stamp along with the event being reserved.

When an event is not interrupted, the write stamp is always the time of the
last event written to the buffer.

In path 1, there's two sub paths we care about:

 a) The event did not interrupt another event.
 b) The event interrupted another event.

In case a, as the write stamp was read and known to be correct, the delta
between the current time stamp and the write stamp is the delta between the
current event and the previously recorded event.

In case b, extra space was reserved to just put the full time stamp into the
buffer. Which is done, as stated, in this path the time stamp taken is known
to match the location in the buffer.

In path 2, there's also two sub paths we care about:

 a) The event was not interrupted by another event since it reserved space
    on the buffer and re-reading the write stamp.
 b) The event was interrupted by another event.

In case a, the write stamp is that of the last event that interrupted this
event between taking the time stamps and reserving. As no event came in
after re-reading the write stamp, that event is known to be the time of the
event directly before this event and the delta can be the new time stamp and
the write stamp.

In case b, one or more events came in between reserving the event and
re-reading he write stamp. Since this event's buffer reservation is between
other events at this path, there's no way to know what the delta is. But
because an event interrupted this event after it started, its fine to just
give a zero delta, and take the same time stamp as the events that happened
within the event being recorded.

Here's the implementation of the design of this solution:

 All this is per cpu, and only needs to worry about nested events (not
 parallel events).

The players:

 write_tail: The index in the buffer where new events can be written to.
     It is incremented via local_add() to reserve space for a new event.

 before_stamp: A time stamp set by all events before reserving space.

 write_stamp: A time stamp updated by events after it has successfully
     reserved space.

	/* Save the current position of write */
 [A]	w = local_read(write_tail);
	barrier();
	/* Read both before and write stamps before touching anything */
	before = local_read(before_stamp);
	after = local_read(write_stamp);
	barrier();

	/*
	 * If before and after are the same, then this event is not
	 * interrupting a time update. If it is, then reserve space for adding
	 * a full time stamp (this can turn into a time extend which is
	 * just an extended time delta but fill up the extra space).
	 */
	if (after != before)
		abs = true;

	ts = clock();

	/* Now update the before_stamp (everyone does this!) */
 [B]	local_set(before_stamp, ts);

	/* Now reserve space on the buffer */
 [C]	write = local_add_return(len, write_tail);

	/* Set tail to be were this event's data is */
	tail = write - len;

 	if (w == tail) {

		/* Nothing interrupted this between A and C */
 [D]		local_set(write_stamp, ts);
		barrier();
 [E]		save_before = local_read(before_stamp);

 		if (!abs) {
			/* This did not interrupt a time update */
			delta = ts - after;
		} else {
			delta = ts; /* The full time stamp will be in use */
		}
		if (ts != save_before) {
			/* slow path - Was interrupted between C and E */
			/* The update to write_stamp could have overwritten the update to
			 * it by the interrupting event, but before and after should be
			 * the same for all completed top events */
			after = local_read(write_stamp);
			if (save_before > after)
				local_cmpxchg(write_stamp, after, save_before);
		}
	} else {
		/* slow path - Interrupted between A and C */

		after = local_read(write_stamp);
		temp_ts = clock();
		barrier();
 [F]		if (write == local_read(write_tail) && after < temp_ts) {
			/* This was not interrupted since C and F
			 * The last write_stamp is still valid for the previous event
			 * in the buffer. */
			delta = temp_ts - after;
			/* OK to keep this new time stamp */
			ts = temp_ts;
		} else {
			/* Interrupted between C and F
			 * Well, there's no use to try to know what the time stamp
			 * is for the previous event. Just set delta to zero and
			 * be the same time as that event that interrupted us before
			 * the reservation of the buffer. */

			delta = 0;
		}
		/* No need to use full timestamps here */
		abs = 0;
	}

Link: https://lkml.kernel.org/r/20200625094454.732790f7@oasis.local.home
Link: https://lore.kernel.org/r/20200627010041.517736087@goodmis.org
Link: http://lkml.kernel.org/r/20200629025258.957440797@goodmis.org

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 276 ++++++++++++++++++++++++-------------
 1 file changed, 181 insertions(+), 95 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 00867ff82412..026238c55b0c 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -27,6 +27,7 @@
 #include <linux/oom.h>
 
 #include <asm/local.h>
+#include <asm/local64.h>
 
 static void update_pages_handler(struct work_struct *work);
 
@@ -418,6 +419,17 @@ struct rb_event_info {
 	int			add_timestamp;
 };
 
+/*
+ * Used for the add_timestamp
+ *  NONE
+ *  NORMAL - may be for either time extend or absolute
+ *  FORCE - force a full time stamp.
+ */
+enum {
+	RB_ADD_STAMP_NONE,
+	RB_ADD_STAMP_NORMAL,
+	RB_ADD_STAMP_FORCE
+};
 /*
  * Used for which event context the event is in.
  *  NMI     = 0
@@ -470,7 +482,8 @@ struct ring_buffer_per_cpu {
 	size_t				shortest_full;
 	unsigned long			read;
 	unsigned long			read_bytes;
-	u64				write_stamp;
+	local64_t			write_stamp;
+	local64_t			before_stamp;
 	u64				read_stamp;
 	/* ring buffer pages to update, > 0 to add, < 0 to remove */
 	long				nr_pages_to_update;
@@ -2416,16 +2429,13 @@ rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
 	unsigned length = info->length;
 	u64 delta = info->delta;
 
-	/* Only a commit updates the timestamp */
-	if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
-		delta = 0;
-
 	/*
 	 * If we need to add a timestamp, then we
 	 * add it to the start of the reserved space.
 	 */
 	if (unlikely(info->add_timestamp)) {
-		bool abs = ring_buffer_time_stamp_abs(cpu_buffer->buffer);
+		bool abs = info->add_timestamp == RB_ADD_STAMP_FORCE ||
+			ring_buffer_time_stamp_abs(cpu_buffer->buffer);
 
 		event = rb_add_time_stamp(event, abs ? info->delta : delta, abs);
 		length -= RB_LEN_TIME_EXTEND;
@@ -2480,6 +2490,39 @@ static inline bool sched_clock_stable(void)
 }
 #endif
 
+static __always_inline bool
+rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
+		   struct ring_buffer_event *event)
+{
+	unsigned long addr = (unsigned long)event;
+	unsigned long index;
+
+	index = rb_event_index(event);
+	addr &= PAGE_MASK;
+
+	return cpu_buffer->commit_page->page == (void *)addr &&
+		rb_commit_index(cpu_buffer) == index;
+}
+
+static u64 rb_time_delta(struct ring_buffer_event *event)
+{
+	switch (event->type_len) {
+	case RINGBUF_TYPE_PADDING:
+		return 0;
+
+	case RINGBUF_TYPE_TIME_EXTEND:
+		return ring_buffer_event_time_stamp(event);
+
+	case RINGBUF_TYPE_TIME_STAMP:
+		return 0;
+
+	case RINGBUF_TYPE_DATA:
+		return event->time_delta;
+	default:
+		return 0;
+	}
+}
+
 static inline int
 rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
 		  struct ring_buffer_event *event)
@@ -2488,6 +2531,8 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
 	struct buffer_page *bpage;
 	unsigned long index;
 	unsigned long addr;
+	u64 write_stamp;
+	u64 delta;
 
 	new_index = rb_event_index(event);
 	old_index = new_index + rb_event_ts_length(event);
@@ -2496,10 +2541,32 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
 
 	bpage = READ_ONCE(cpu_buffer->tail_page);
 
+	delta = rb_time_delta(event);
+
+	write_stamp = local64_read(&cpu_buffer->write_stamp);
+
+	/* Make sure the write stamp is read before testing the location */
+	barrier();
+
 	if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
 		unsigned long write_mask =
 			local_read(&bpage->write) & ~RB_WRITE_MASK;
 		unsigned long event_length = rb_event_length(event);
+		u64 ret;
+
+		ret = local64_cmpxchg(&cpu_buffer->write_stamp, write_stamp, write_stamp - delta);
+		/* Something came in, can't discard */
+		if (ret != write_stamp)
+			return 0;
+
+		/*
+		 * If an event were to come in now, it would see that the
+		 * write_stamp and the before_stamp are different, and assume
+		 * that this event just added itself before updating
+		 * the write stamp. The interrupting event will fix the
+		 * write stamp for us, and use the before stamp as its delta.
+		 */
+
 		/*
 		 * This is on the tail page. It is possible that
 		 * a write could come in and move the tail page
@@ -2551,10 +2618,6 @@ rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
 		local_set(&cpu_buffer->commit_page->page->commit,
 			  rb_page_write(cpu_buffer->commit_page));
 		rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
-		/* Only update the write stamp if the page has an event */
-		if (rb_page_write(cpu_buffer->commit_page))
-			cpu_buffer->write_stamp =
-				cpu_buffer->commit_page->page->time_stamp;
 		/* add barrier to keep gcc from optimizing too much */
 		barrier();
 	}
@@ -2626,54 +2689,10 @@ static inline void rb_event_discard(struct ring_buffer_event *event)
 		event->time_delta = 1;
 }
 
-static __always_inline bool
-rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
-		   struct ring_buffer_event *event)
-{
-	unsigned long addr = (unsigned long)event;
-	unsigned long index;
-
-	index = rb_event_index(event);
-	addr &= PAGE_MASK;
-
-	return cpu_buffer->commit_page->page == (void *)addr &&
-		rb_commit_index(cpu_buffer) == index;
-}
-
-static __always_inline void
-rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
-		      struct ring_buffer_event *event)
-{
-	u64 delta;
-
-	/*
-	 * The event first in the commit queue updates the
-	 * time stamp.
-	 */
-	if (rb_event_is_commit(cpu_buffer, event)) {
-		/*
-		 * A commit event that is first on a page
-		 * updates the write timestamp with the page stamp
-		 */
-		if (!rb_event_index(event))
-			cpu_buffer->write_stamp =
-				cpu_buffer->commit_page->page->time_stamp;
-		else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
-			delta = ring_buffer_event_time_stamp(event);
-			cpu_buffer->write_stamp += delta;
-		} else if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
-			delta = ring_buffer_event_time_stamp(event);
-			cpu_buffer->write_stamp = delta;
-		} else
-			cpu_buffer->write_stamp += event->time_delta;
-	}
-}
-
 static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
 		      struct ring_buffer_event *event)
 {
 	local_inc(&cpu_buffer->entries);
-	rb_update_write_stamp(cpu_buffer, event);
 	rb_end_commit(cpu_buffer);
 }
 
@@ -2872,13 +2891,13 @@ rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 		  KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
 		  (unsigned long long)info->delta,
 		  (unsigned long long)info->ts,
-		  (unsigned long long)cpu_buffer->write_stamp,
+		  (unsigned long long)local64_read(&cpu_buffer->write_stamp),
 		  sched_clock_stable() ? "" :
 		  "If you just came from a suspend/resume,\n"
 		  "please switch to the trace global clock:\n"
 		  "  echo global > /sys/kernel/debug/tracing/trace_clock\n"
 		  "or add trace_clock=global to the kernel command line\n");
-	info->add_timestamp = 1;
+	info->add_timestamp = RB_ADD_STAMP_NORMAL;
 }
 
 static struct ring_buffer_event *
@@ -2887,8 +2906,36 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 {
 	struct ring_buffer_event *event;
 	struct buffer_page *tail_page;
-	unsigned long tail, write;
+	unsigned long tail, write, w;
+	u64 before, after;
+	bool abs = false;
+
+	/* Don't let the compiler play games with cpu_buffer->tail_page */
+	tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
+
+ /*A*/	w = local_read(&tail_page->write) & RB_WRITE_MASK;
+	barrier();
+	before = local64_read(&cpu_buffer->before_stamp);
+	after = local64_read(&cpu_buffer->write_stamp);
+	barrier();
+	info->ts = rb_time_stamp(cpu_buffer->buffer);
+
+	if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
+		info->delta = info->ts;
+		abs = true;
+	} else {
+		info->delta = info->ts - after;
+	}
+
+	if (unlikely(test_time_stamp(info->delta)))
+		rb_handle_timestamp(cpu_buffer, info);
 
+	/*
+	 * If interrupting an event time update, we may need an absolute timestamp.
+	 * Don't bother if this is the start of a new page (w == 0).
+	 */
+	if (unlikely(before != after && w))
+		info->add_timestamp = RB_ADD_STAMP_FORCE;
 	/*
 	 * If the time delta since the last event is too big to
 	 * hold in the time field of the event, then we append a
@@ -2897,25 +2944,88 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	if (unlikely(info->add_timestamp))
 		info->length += RB_LEN_TIME_EXTEND;
 
-	/* Don't let the compiler play games with cpu_buffer->tail_page */
-	tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
-	write = local_add_return(info->length, &tail_page->write);
+ /*B*/	local64_set(&cpu_buffer->before_stamp, info->ts);
+
+ /*C*/	write = local_add_return(info->length, &tail_page->write);
 
 	/* set write to only the index of the write */
 	write &= RB_WRITE_MASK;
+
 	tail = write - info->length;
 
+	/* See if we shot pass the end of this buffer page */
+	if (unlikely(write > BUF_PAGE_SIZE)) {
+		if (tail != w) {
+			/* before and after may now different, fix it up*/
+			before = local64_read(&cpu_buffer->before_stamp);
+			after = local64_read(&cpu_buffer->write_stamp);
+			if (before != after)
+				(void)local64_cmpxchg(&cpu_buffer->before_stamp, before, after);
+		}
+		return rb_move_tail(cpu_buffer, tail, info);
+	}
+
+	if (likely(tail == w)) {
+		u64 save_before;
+
+		/* Nothing interrupted us between A and C */
+ /*D*/		local64_set(&cpu_buffer->write_stamp, info->ts);
+		barrier();
+ /*E*/		save_before = local64_read(&cpu_buffer->before_stamp);
+		if (likely(info->add_timestamp != RB_ADD_STAMP_FORCE))
+			/* This did not interrupt any time update */
+			info->delta = info->ts - after;
+		else
+			/* Just use full timestamp for inerrupting event */
+			info->delta = info->ts;
+		barrier();
+		if (unlikely(info->ts != save_before)) {
+			/* SLOW PATH - Interrupted between C and E */
+
+			after = local64_read(&cpu_buffer->write_stamp);
+			/* Write stamp must only go forward */
+			if (save_before > after) {
+				/*
+				 * We do not care about the result, only that
+				 * it gets updated atomically.
+				 */
+				(void)local64_cmpxchg(&cpu_buffer->write_stamp, after, save_before);
+			}
+		}
+	} else {
+		u64 ts;
+		/* SLOW PATH - Interrupted between A and C */
+		after = local64_read(&cpu_buffer->write_stamp);
+		ts = rb_time_stamp(cpu_buffer->buffer);
+		barrier();
+ /*E*/		if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
+		    after < ts) {
+			/* Nothing came after this event between C and E */
+			info->delta = ts - after;
+			(void)local64_cmpxchg(&cpu_buffer->write_stamp, after, info->ts);
+			info->ts = ts;
+		} else {
+			/*
+			 * Interrupted beween C and E:
+			 * Lost the previous events time stamp. Just set the
+			 * delta to zero, and this will be the same time as
+			 * the event this event interrupted. And the events that
+			 * came after this will still be correct (as they would
+			 * have built their delta on the previous event.
+			 */
+			info->delta = 0;
+		}
+		if (info->add_timestamp == RB_ADD_STAMP_FORCE)
+			info->add_timestamp = RB_ADD_STAMP_NORMAL;
+	}
+
 	/*
 	 * If this is the first commit on the page, then it has the same
 	 * timestamp as the page itself.
 	 */
-	if (!tail && !ring_buffer_time_stamp_abs(cpu_buffer->buffer))
+	if (unlikely(!tail && info->add_timestamp != RB_ADD_STAMP_FORCE && !abs))
 		info->delta = 0;
 
-	/* See if we shot pass the end of this buffer page */
-	if (unlikely(write > BUF_PAGE_SIZE))
-		return rb_move_tail(cpu_buffer, tail, info);
-
 	/* We reserved something on the buffer */
 
 	event = __rb_page_index(tail_page, tail);
@@ -2944,9 +3054,9 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 	struct ring_buffer_event *event;
 	struct rb_event_info info;
 	int nr_loops = 0;
-	u64 diff;
 
 	rb_start_commit(cpu_buffer);
+	/* The commit page can not change after this */
 
 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 	/*
@@ -2965,7 +3075,7 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 
 	info.length = rb_calculate_event_length(length);
  again:
-	info.add_timestamp = 0;
+	info.add_timestamp = RB_ADD_STAMP_NONE;
 	info.delta = 0;
 
 	/*
@@ -2980,22 +3090,6 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
 		goto out_fail;
 
-	info.ts = rb_time_stamp(cpu_buffer->buffer);
-	diff = info.ts - cpu_buffer->write_stamp;
-
-	/* make sure this diff is calculated here */
-	barrier();
-
-	if (ring_buffer_time_stamp_abs(buffer)) {
-		info.delta = info.ts;
-		rb_handle_timestamp(cpu_buffer, &info);
-	} else /* Did the write stamp get updated already? */
-		if (likely(info.ts >= cpu_buffer->write_stamp)) {
-		info.delta = diff;
-		if (unlikely(test_time_stamp(info.delta)))
-			rb_handle_timestamp(cpu_buffer, &info);
-	}
-
 	event = __rb_reserve_next(cpu_buffer, &info);
 
 	if (unlikely(PTR_ERR(event) == -EAGAIN)) {
@@ -3004,11 +3098,8 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 		goto again;
 	}
 
-	if (!event)
-		goto out_fail;
-
-	return event;
-
+	if (likely(event))
+		return event;
  out_fail:
 	rb_end_commit(cpu_buffer);
 	return NULL;
@@ -3154,11 +3245,6 @@ void ring_buffer_discard_commit(struct trace_buffer *buffer,
 	if (rb_try_to_discard(cpu_buffer, event))
 		goto out;
 
-	/*
-	 * The commit is still visible by the reader, so we
-	 * must still update the timestamp.
-	 */
-	rb_update_write_stamp(cpu_buffer, event);
  out:
 	rb_end_commit(cpu_buffer);
 
@@ -4475,8 +4561,8 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 	cpu_buffer->read = 0;
 	cpu_buffer->read_bytes = 0;
 
-	cpu_buffer->write_stamp = 0;
-	cpu_buffer->read_stamp = 0;
+	local64_set(&cpu_buffer->write_stamp, 0);
+	local64_set(&cpu_buffer->before_stamp, 0);
 
 	cpu_buffer->lost_events = 0;
 	cpu_buffer->last_overrun = 0;
-- 
2.26.2

[for-next][PATCH 11/18] ring-buffer: Incorporate absolute timestamp into add_timestamp logic

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Instead of calling out the absolute test for each time to check if the
ring buffer wants absolute time stamps for all its recording, incorporate it
with the add_timestamp field and turn it into flags for faster processing
between wanting a absolute tag and needing to force one.

Link: http://lkml.kernel.org/r/20200629025259.154892368@goodmis.org

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 40 +++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 18 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 026238c55b0c..7ee6619951ea 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -422,13 +422,15 @@ struct rb_event_info {
 /*
  * Used for the add_timestamp
  *  NONE
- *  NORMAL - may be for either time extend or absolute
+ *  EXTEND - wants a time extend
+ *  ABSOLUTE - the buffer requests all events to have absolute time stamps
  *  FORCE - force a full time stamp.
  */
 enum {
-	RB_ADD_STAMP_NONE,
-	RB_ADD_STAMP_NORMAL,
-	RB_ADD_STAMP_FORCE
+	RB_ADD_STAMP_NONE		= 0,
+	RB_ADD_STAMP_EXTEND		= BIT(1),
+	RB_ADD_STAMP_ABSOLUTE		= BIT(2),
+	RB_ADD_STAMP_FORCE		= BIT(3)
 };
 /*
  * Used for which event context the event is in.
@@ -2434,8 +2436,8 @@ rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
 	 * add it to the start of the reserved space.
 	 */
 	if (unlikely(info->add_timestamp)) {
-		bool abs = info->add_timestamp == RB_ADD_STAMP_FORCE ||
-			ring_buffer_time_stamp_abs(cpu_buffer->buffer);
+		bool abs = info->add_timestamp &
+			(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
 
 		event = rb_add_time_stamp(event, abs ? info->delta : delta, abs);
 		length -= RB_LEN_TIME_EXTEND;
@@ -2884,8 +2886,8 @@ int ring_buffer_unlock_commit(struct trace_buffer *buffer,
 EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
 
 static noinline void
-rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
-		    struct rb_event_info *info)
+rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
+		   struct rb_event_info *info)
 {
 	WARN_ONCE(info->delta > (1ULL << 59),
 		  KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
@@ -2897,7 +2899,6 @@ rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 		  "please switch to the trace global clock:\n"
 		  "  echo global > /sys/kernel/debug/tracing/trace_clock\n"
 		  "or add trace_clock=global to the kernel command line\n");
-	info->add_timestamp = RB_ADD_STAMP_NORMAL;
 }
 
 static struct ring_buffer_event *
@@ -2908,7 +2909,6 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	struct buffer_page *tail_page;
 	unsigned long tail, write, w;
 	u64 before, after;
-	bool abs = false;
 
 	/* Don't let the compiler play games with cpu_buffer->tail_page */
 	tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
@@ -2922,20 +2922,23 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 
 	if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
 		info->delta = info->ts;
-		abs = true;
+		info->add_timestamp = RB_ADD_STAMP_ABSOLUTE;
 	} else {
 		info->delta = info->ts - after;
 	}
 
-	if (unlikely(test_time_stamp(info->delta)))
-		rb_handle_timestamp(cpu_buffer, info);
+	if (unlikely(test_time_stamp(info->delta))) {
+		rb_check_timestamp(cpu_buffer, info);
+		info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+	}
 
 	/*
 	 * If interrupting an event time update, we may need an absolute timestamp.
 	 * Don't bother if this is the start of a new page (w == 0).
 	 */
 	if (unlikely(before != after && w))
-		info->add_timestamp = RB_ADD_STAMP_FORCE;
+		info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
+
 	/*
 	 * If the time delta since the last event is too big to
 	 * hold in the time field of the event, then we append a
@@ -2972,7 +2975,8 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
  /*D*/		local64_set(&cpu_buffer->write_stamp, info->ts);
 		barrier();
  /*E*/		save_before = local64_read(&cpu_buffer->before_stamp);
-		if (likely(info->add_timestamp != RB_ADD_STAMP_FORCE))
+		if (likely(!(info->add_timestamp &
+			     (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
 			/* This did not interrupt any time update */
 			info->delta = info->ts - after;
 		else
@@ -3015,15 +3019,15 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 			 */
 			info->delta = 0;
 		}
-		if (info->add_timestamp == RB_ADD_STAMP_FORCE)
-			info->add_timestamp = RB_ADD_STAMP_NORMAL;
+		info->add_timestamp &= ~RB_ADD_STAMP_FORCE;
 	}
 
 	/*
 	 * If this is the first commit on the page, then it has the same
 	 * timestamp as the page itself.
 	 */
-	if (unlikely(!tail && info->add_timestamp != RB_ADD_STAMP_FORCE && !abs))
+	if (unlikely(!tail && !(info->add_timestamp &
+				(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
 		info->delta = 0;
 
 	/* We reserved something on the buffer */
-- 
2.26.2

[for-next][PATCH 12/18] ring-buffer: Add rb_time_t 64 bit operations for speeding up 32 bit

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

After a discussion with the new time algorithm to have nested events still
have proper time keeping but required using local64_t atomic operations.
Mathieu was concerned about the performance this would have on 32 bit
machines, as in most cases, atomic 64 bit operations on them can be
expensive.

As the ring buffer's timing needs do not require full features of local64_t,
a wrapper is made to implement a new rb_time_t operation that uses two longs
on 32 bit machines but still uses the local64_t operations on 64 bit
machines. There's a switch that can be made in the file to force 64 bit to
use the 32 bit version just for testing purposes.

All reads do not need to succeed if a read happened while the stamp being
read is in the process of being updated. The requirement is that all reads
must succed that were done by an interrupting event (where this event was
interrupted by another event that did the write). Or if the event itself did
the write first. That is: rb_time_set(t, x) followed by rb_time_read(t) will
always succeed (even if it gets interrupted by another event that writes to
t. The result of the read will be either the previous set, or a set
performed by an interrupting event.

If the read is done by an event that interrupted another event that was in
the process of setting the time stamp, and no other event came along to
write to that time stamp, it will fail and the rb_time_read() will return
that it failed (the value to read will be undefined).

A set will always write to the time stamp and return with a valid time
stamp, such that any read after it will be valid.

A cmpxchg may fail if it interrupted an event that was in the process of
updating the time stamp just like the reads do. Other than that, it will act
like a normal cmpxchg.

The way this works is that the rb_time_t is made of of three fields. A cnt,
that gets updated atomically everyting a modification is made. A top that
represents the most significant 30 bits of the time, and a bottom to
represent the least significant 30 bits of the time. Notice, that the time
values is only 60 bits long (where the ring buffer only uses 59 bits, which
gives us 18 years of nanoseconds!).

The top two bits of both the top and bottom is a 2 bit counter that gets set
by the value of the least two significant bits of the cnt. A read of the top
and the bottom where both the top and bottom have the same most significant
top 2 bits, are considered a match and a valid 60 bit number can be created
from it. If they do not match, then the number is considered invalid, and
this must only happen if an event interrupted another event in the midst of
updating the time stamp.

This is only used for 32 bits machines as 64 bit machines can get better
performance out of the local64_t. This has been tested heavily by forcing 64
bit to use this logic.

Link: https://lore.kernel.org/r/20200625225345.18cf5881@oasis.local.home
Link: http://lkml.kernel.org/r/20200629025259.309232719@goodmis.org

Inspired-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 270 +++++++++++++++++++++++++++++++++----
 1 file changed, 243 insertions(+), 27 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7ee6619951ea..802bb38d9c81 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -27,7 +27,6 @@
 #include <linux/oom.h>
 
 #include <asm/local.h>
-#include <asm/local64.h>
 
 static void update_pages_handler(struct work_struct *work);
 
@@ -449,6 +448,28 @@ enum {
 	RB_CTX_MAX
 };
 
+#if BITS_PER_LONG == 32
+#define RB_TIME_32
+#endif
+
+/* To test on 64 bit machines */
+//#define RB_TIME_32
+
+#ifdef RB_TIME_32
+
+struct rb_time_struct {
+	local_t		cnt;
+	local_t		top;
+	local_t		bottom;
+};
+#else
+#include <asm/local64.h>
+struct rb_time_struct {
+	local64_t	time;
+};
+#endif
+typedef struct rb_time_struct rb_time_t;
+
 /*
  * head_page == tail_page && head == tail then buffer is empty.
  */
@@ -484,8 +505,8 @@ struct ring_buffer_per_cpu {
 	size_t				shortest_full;
 	unsigned long			read;
 	unsigned long			read_bytes;
-	local64_t			write_stamp;
-	local64_t			before_stamp;
+	rb_time_t			write_stamp;
+	rb_time_t			before_stamp;
 	u64				read_stamp;
 	/* ring buffer pages to update, > 0 to add, < 0 to remove */
 	long				nr_pages_to_update;
@@ -528,6 +549,189 @@ struct ring_buffer_iter {
 	int				missed_events;
 };
 
+#ifdef RB_TIME_32
+
+/*
+ * On 32 bit machines, local64_t is very expensive. As the ring
+ * buffer doesn't need all the features of a true 64 bit atomic,
+ * on 32 bit, it uses these functions (64 still uses local64_t).
+ *
+ * For the ring buffer, 64 bit required operations for the time is
+ * the following:
+ *
+ *  - Only need 59 bits (uses 60 to make it even).
+ *  - Reads may fail if it interrupted a modification of the time stamp.
+ *      It will succeed if it did not interrupt another write even if
+ *      the read itself is interrupted by a write.
+ *      It returns whether it was successful or not.
+ *
+ *  - Writes always succeed and will overwrite other writes and writes
+ *      that were done by events interrupting the current write.
+ *
+ *  - A write followed by a read of the same time stamp will always succeed,
+ *      but may not contain the same value.
+ *
+ *  - A cmpxchg will fail if it interrupted another write or cmpxchg.
+ *      Other than that, it acts like a normal cmpxchg.
+ *
+ * The 60 bit time stamp is broken up by 30 bits in a top and bottom half
+ *  (bottom being the least significant 30 bits of the 60 bit time stamp).
+ *
+ * The two most significant bits of each half holds a 2 bit counter (0-3).
+ * Each update will increment this counter by one.
+ * When reading the top and bottom, if the two counter bits match then the
+ *  top and bottom together make a valid 60 bit number.
+ */
+#define RB_TIME_SHIFT	30
+#define RB_TIME_VAL_MASK ((1 << RB_TIME_SHIFT) - 1)
+
+static inline int rb_time_cnt(unsigned long val)
+{
+	return (val >> RB_TIME_SHIFT) & 3;
+}
+
+static inline u64 rb_time_val(unsigned long top, unsigned long bottom)
+{
+	u64 val;
+
+	val = top & RB_TIME_VAL_MASK;
+	val <<= RB_TIME_SHIFT;
+	val |= bottom & RB_TIME_VAL_MASK;
+
+	return val;
+}
+
+static inline bool __rb_time_read(rb_time_t *t, u64 *ret, unsigned long *cnt)
+{
+	unsigned long top, bottom;
+	unsigned long c;
+
+	/*
+	 * If the read is interrupted by a write, then the cnt will
+	 * be different. Loop until both top and bottom have been read
+	 * without interruption.
+	 */
+	do {
+		c = local_read(&t->cnt);
+		top = local_read(&t->top);
+		bottom = local_read(&t->bottom);
+	} while (c != local_read(&t->cnt));
+
+	*cnt = rb_time_cnt(top);
+
+	/* If top and bottom counts don't match, this interrupted a write */
+	if (*cnt != rb_time_cnt(bottom))
+		return false;
+
+	*ret = rb_time_val(top, bottom);
+	return true;
+}
+
+static bool rb_time_read(rb_time_t *t, u64 *ret)
+{
+	unsigned long cnt;
+
+	return __rb_time_read(t, ret, &cnt);
+}
+
+static inline unsigned long rb_time_val_cnt(unsigned long val, unsigned long cnt)
+{
+	return (val & RB_TIME_VAL_MASK) | ((cnt & 3) << RB_TIME_SHIFT);
+}
+
+static inline void rb_time_split(u64 val, unsigned long *top, unsigned long *bottom)
+{
+	*top = (unsigned long)((val >> RB_TIME_SHIFT) & RB_TIME_VAL_MASK);
+	*bottom = (unsigned long)(val & RB_TIME_VAL_MASK);
+}
+
+static inline void rb_time_val_set(local_t *t, unsigned long val, unsigned long cnt)
+{
+	val = rb_time_val_cnt(val, cnt);
+	local_set(t, val);
+}
+
+static void rb_time_set(rb_time_t *t, u64 val)
+{
+	unsigned long cnt, top, bottom;
+
+	rb_time_split(val, &top, &bottom);
+
+	/* Writes always succeed with a valid number even if it gets interrupted. */
+	do {
+		cnt = local_inc_return(&t->cnt);
+		rb_time_val_set(&t->top, top, cnt);
+		rb_time_val_set(&t->bottom, bottom, cnt);
+	} while (cnt != local_read(&t->cnt));
+}
+
+static inline bool
+rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set)
+{
+	unsigned long ret;
+
+	ret = local_cmpxchg(l, expect, set);
+	return ret == expect;
+}
+
+static int rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
+{
+	unsigned long cnt, top, bottom;
+	unsigned long cnt2, top2, bottom2;
+	u64 val;
+
+	/* The cmpxchg always fails if it interrupted an update */
+	 if (!__rb_time_read(t, &val, &cnt2))
+		 return false;
+
+	 if (val != expect)
+		 return false;
+
+	 cnt = local_read(&t->cnt);
+	 if ((cnt & 3) != cnt2)
+		 return false;
+
+	 cnt2 = cnt + 1;
+
+	 rb_time_split(val, &top, &bottom);
+	 top = rb_time_val_cnt(top, cnt);
+	 bottom = rb_time_val_cnt(bottom, cnt);
+
+	 rb_time_split(set, &top2, &bottom2);
+	 top2 = rb_time_val_cnt(top2, cnt2);
+	 bottom2 = rb_time_val_cnt(bottom2, cnt2);
+
+	if (!rb_time_read_cmpxchg(&t->cnt, cnt, cnt2))
+		return false;
+	if (!rb_time_read_cmpxchg(&t->top, top, top2))
+		return false;
+	if (!rb_time_read_cmpxchg(&t->bottom, bottom, bottom2))
+		return false;
+	return true;
+}
+
+#else /* 64 bits */
+
+/* local64_t always succeeds */
+
+static inline bool rb_time_read(rb_time_t *t, u64 *ret)
+{
+	*ret = local64_read(&t->time);
+	return true;
+}
+static void rb_time_set(rb_time_t *t, u64 val)
+{
+	local64_set(&t->time, val);
+}
+
+static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
+{
+	u64 val;
+	val = local64_cmpxchg(&t->time, expect, set);
+	return val == expect;
+}
+#endif
+
 /**
  * ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
  * @buffer: The ring_buffer to get the number of pages from
@@ -2545,7 +2749,8 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
 
 	delta = rb_time_delta(event);
 
-	write_stamp = local64_read(&cpu_buffer->write_stamp);
+	if (!rb_time_read(&cpu_buffer->write_stamp, &write_stamp))
+		return 0;
 
 	/* Make sure the write stamp is read before testing the location */
 	barrier();
@@ -2554,11 +2759,10 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
 		unsigned long write_mask =
 			local_read(&bpage->write) & ~RB_WRITE_MASK;
 		unsigned long event_length = rb_event_length(event);
-		u64 ret;
 
-		ret = local64_cmpxchg(&cpu_buffer->write_stamp, write_stamp, write_stamp - delta);
 		/* Something came in, can't discard */
-		if (ret != write_stamp)
+		if (!rb_time_cmpxchg(&cpu_buffer->write_stamp,
+				       write_stamp, write_stamp - delta))
 			return 0;
 
 		/*
@@ -2889,11 +3093,13 @@ static noinline void
 rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 		   struct rb_event_info *info)
 {
+	u64 write_stamp;
+
 	WARN_ONCE(info->delta > (1ULL << 59),
 		  KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
 		  (unsigned long long)info->delta,
 		  (unsigned long long)info->ts,
-		  (unsigned long long)local64_read(&cpu_buffer->write_stamp),
+		  (unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
 		  sched_clock_stable() ? "" :
 		  "If you just came from a suspend/resume,\n"
 		  "please switch to the trace global clock:\n"
@@ -2909,14 +3115,16 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	struct buffer_page *tail_page;
 	unsigned long tail, write, w;
 	u64 before, after;
+	bool a_ok;
+	bool b_ok;
 
 	/* Don't let the compiler play games with cpu_buffer->tail_page */
 	tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
 
  /*A*/	w = local_read(&tail_page->write) & RB_WRITE_MASK;
 	barrier();
-	before = local64_read(&cpu_buffer->before_stamp);
-	after = local64_read(&cpu_buffer->write_stamp);
+	b_ok = rb_time_read(&cpu_buffer->before_stamp, &before);
+	a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
 	barrier();
 	info->ts = rb_time_stamp(cpu_buffer->buffer);
 
@@ -2927,16 +3135,18 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		info->delta = info->ts - after;
 	}
 
-	if (unlikely(test_time_stamp(info->delta))) {
-		rb_check_timestamp(cpu_buffer, info);
-		info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+	if (likely(a_ok && b_ok)) {
+		if (unlikely(test_time_stamp(info->delta))) {
+			rb_check_timestamp(cpu_buffer, info);
+			info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+		}
 	}
 
 	/*
 	 * If interrupting an event time update, we may need an absolute timestamp.
 	 * Don't bother if this is the start of a new page (w == 0).
 	 */
-	if (unlikely(before != after && w))
+	if (unlikely(!a_ok || !b_ok || (before != after && w)))
 		info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
 
 	/*
@@ -2947,7 +3157,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	if (unlikely(info->add_timestamp))
 		info->length += RB_LEN_TIME_EXTEND;
 
- /*B*/	local64_set(&cpu_buffer->before_stamp, info->ts);
+ /*B*/	rb_time_set(&cpu_buffer->before_stamp, info->ts);
 
  /*C*/	write = local_add_return(info->length, &tail_page->write);
 
@@ -2960,21 +3170,23 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	if (unlikely(write > BUF_PAGE_SIZE)) {
 		if (tail != w) {
 			/* before and after may now different, fix it up*/
-			before = local64_read(&cpu_buffer->before_stamp);
-			after = local64_read(&cpu_buffer->write_stamp);
-			if (before != after)
-				(void)local64_cmpxchg(&cpu_buffer->before_stamp, before, after);
+			b_ok = rb_time_read(&cpu_buffer->before_stamp, &before);
+			a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+			if (a_ok && b_ok && before != after)
+				(void)rb_time_cmpxchg(&cpu_buffer->before_stamp, before, after);
 		}
 		return rb_move_tail(cpu_buffer, tail, info);
 	}
 
 	if (likely(tail == w)) {
 		u64 save_before;
+		bool s_ok;
 
 		/* Nothing interrupted us between A and C */
- /*D*/		local64_set(&cpu_buffer->write_stamp, info->ts);
+ /*D*/		rb_time_set(&cpu_buffer->write_stamp, info->ts);
 		barrier();
- /*E*/		save_before = local64_read(&cpu_buffer->before_stamp);
+ /*E*/		s_ok = rb_time_read(&cpu_buffer->before_stamp, &save_before);
+		RB_WARN_ON(cpu_buffer, !s_ok);
 		if (likely(!(info->add_timestamp &
 			     (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
 			/* This did not interrupt any time update */
@@ -2986,27 +3198,31 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		if (unlikely(info->ts != save_before)) {
 			/* SLOW PATH - Interrupted between C and E */
 
-			after = local64_read(&cpu_buffer->write_stamp);
+			a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+			RB_WARN_ON(cpu_buffer, !a_ok);
+
 			/* Write stamp must only go forward */
 			if (save_before > after) {
 				/*
 				 * We do not care about the result, only that
 				 * it gets updated atomically.
 				 */
-				(void)local64_cmpxchg(&cpu_buffer->write_stamp, after, save_before);
+				(void)rb_time_cmpxchg(&cpu_buffer->write_stamp, after, save_before);
 			}
 		}
 	} else {
 		u64 ts;
 		/* SLOW PATH - Interrupted between A and C */
-		after = local64_read(&cpu_buffer->write_stamp);
+		a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+		/* Was interrupted before here, write_stamp must be valid */
+		RB_WARN_ON(cpu_buffer, !a_ok);
 		ts = rb_time_stamp(cpu_buffer->buffer);
 		barrier();
  /*E*/		if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
 		    after < ts) {
 			/* Nothing came after this event between C and E */
 			info->delta = ts - after;
-			(void)local64_cmpxchg(&cpu_buffer->write_stamp, after, info->ts);
+			(void)rb_time_cmpxchg(&cpu_buffer->write_stamp, after, info->ts);
 			info->ts = ts;
 		} else {
 			/*
@@ -4565,8 +4781,8 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 	cpu_buffer->read = 0;
 	cpu_buffer->read_bytes = 0;
 
-	local64_set(&cpu_buffer->write_stamp, 0);
-	local64_set(&cpu_buffer->before_stamp, 0);
+	rb_time_set(&cpu_buffer->write_stamp, 0);
+	rb_time_set(&cpu_buffer->before_stamp, 0);
 
 	cpu_buffer->lost_events = 0;
 	cpu_buffer->last_overrun = 0;
-- 
2.26.2

[for-next][PATCH 13/18] ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU

[Steven Rostedt]

From: Nicholas Piggin <npiggin@gmail.com>

On a 144 thread system, `perf ftrace` takes about 20 seconds to start
up, due to calling synchronize_rcu() for each CPU.

  cat /proc/108560/stack
    0xc0003e7eb336f470
    __switch_to+0x2e0/0x480
    __wait_rcu_gp+0x20c/0x220
    synchronize_rcu+0x9c/0xc0
    ring_buffer_reset_cpu+0x88/0x2e0
    tracing_reset_online_cpus+0x84/0xe0
    tracing_open+0x1d4/0x1f0

On a system with 10x more threads, it starts to become an annoyance.

Batch these up so we disable all the per-cpu buffers first, then
synchronize_rcu() once, then reset each of the buffers. This brings
the time down to about 0.5s.

Link: https://lkml.kernel.org/r/20200625053403.2386972-1-npiggin@gmail.com

Tested-by: Anton Blanchard <anton@ozlabs.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/ring_buffer.h |  1 +
 kernel/trace/ring_buffer.c  | 85 +++++++++++++++++++++++++++++++------
 kernel/trace/trace.c        |  4 +-
 3 files changed, 73 insertions(+), 17 deletions(-)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index c76b2f3b3ac4..136ea0997e6d 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -143,6 +143,7 @@ bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter);
 unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu);
 
 void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu);
+void ring_buffer_reset_online_cpus(struct trace_buffer *buffer);
 void ring_buffer_reset(struct trace_buffer *buffer);
 
 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 802bb38d9c81..ed1941304f69 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -270,6 +270,9 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
 #define for_each_buffer_cpu(buffer, cpu)		\
 	for_each_cpu(cpu, buffer->cpumask)
 
+#define for_each_online_buffer_cpu(buffer, cpu)		\
+	for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
+
 #define TS_SHIFT	27
 #define TS_MASK		((1ULL << TS_SHIFT) - 1)
 #define TS_DELTA_TEST	(~TS_MASK)
@@ -4790,6 +4793,26 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 	rb_head_page_activate(cpu_buffer);
 }
 
+/* Must have disabled the cpu buffer then done a synchronize_rcu */
+static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
+		goto out;
+
+	arch_spin_lock(&cpu_buffer->lock);
+
+	rb_reset_cpu(cpu_buffer);
+
+	arch_spin_unlock(&cpu_buffer->lock);
+
+ out:
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+}
+
 /**
  * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
  * @buffer: The ring buffer to reset a per cpu buffer of
@@ -4798,7 +4821,6 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
-	unsigned long flags;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return;
@@ -4809,24 +4831,42 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
 	/* Make sure all commits have finished */
 	synchronize_rcu();
 
-	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	reset_disabled_cpu_buffer(cpu_buffer);
 
-	if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
-		goto out;
+	atomic_dec(&cpu_buffer->record_disabled);
+	atomic_dec(&cpu_buffer->resize_disabled);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
 
-	arch_spin_lock(&cpu_buffer->lock);
+/**
+ * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
+ * @buffer: The ring buffer to reset a per cpu buffer of
+ * @cpu: The CPU buffer to be reset
+ */
+void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	int cpu;
 
-	rb_reset_cpu(cpu_buffer);
+	for_each_online_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
 
-	arch_spin_unlock(&cpu_buffer->lock);
+		atomic_inc(&cpu_buffer->resize_disabled);
+		atomic_inc(&cpu_buffer->record_disabled);
+	}
 
- out:
-	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	/* Make sure all commits have finished */
+	synchronize_rcu();
 
-	atomic_dec(&cpu_buffer->record_disabled);
-	atomic_dec(&cpu_buffer->resize_disabled);
+	for_each_online_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		reset_disabled_cpu_buffer(cpu_buffer);
+
+		atomic_dec(&cpu_buffer->record_disabled);
+		atomic_dec(&cpu_buffer->resize_disabled);
+	}
 }
-EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
 
 /**
  * ring_buffer_reset - reset a ring buffer
@@ -4834,10 +4874,27 @@ EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
  */
 void ring_buffer_reset(struct trace_buffer *buffer)
 {
+	struct ring_buffer_per_cpu *cpu_buffer;
 	int cpu;
 
-	for_each_buffer_cpu(buffer, cpu)
-		ring_buffer_reset_cpu(buffer, cpu);
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		atomic_inc(&cpu_buffer->resize_disabled);
+		atomic_inc(&cpu_buffer->record_disabled);
+	}
+
+	/* Make sure all commits have finished */
+	synchronize_rcu();
+
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		reset_disabled_cpu_buffer(cpu_buffer);
+
+		atomic_dec(&cpu_buffer->record_disabled);
+		atomic_dec(&cpu_buffer->resize_disabled);
+	}
 }
 EXPORT_SYMBOL_GPL(ring_buffer_reset);
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 64c5b8146cca..4aab712f9567 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2003,7 +2003,6 @@ static void tracing_reset_cpu(struct array_buffer *buf, int cpu)
 void tracing_reset_online_cpus(struct array_buffer *buf)
 {
 	struct trace_buffer *buffer = buf->buffer;
-	int cpu;
 
 	if (!buffer)
 		return;
@@ -2015,8 +2014,7 @@ void tracing_reset_online_cpus(struct array_buffer *buf)
 
 	buf->time_start = buffer_ftrace_now(buf, buf->cpu);
 
-	for_each_online_cpu(cpu)
-		ring_buffer_reset_cpu(buffer, cpu);
+	ring_buffer_reset_online_cpus(buffer);
 
 	ring_buffer_record_enable(buffer);
 }
-- 
2.26.2

[for-next][PATCH 14/18] ring-buffer: Mark the !tail (crossing a page) as unlikely

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

It is the uncommon case where an event crosses a sub buffer boundary (page)
mark that check at the end of reserving an event as unlikely.

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ed1941304f69..888bc9177937 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3260,7 +3260,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	 * If this is the first commit on the page, then update
 	 * its timestamp.
 	 */
-	if (!tail)
+	if (unlikely(!tail))
 		tail_page->page->time_stamp = info->ts;
 
 	/* account for these added bytes */
-- 
2.26.2

[for-next][PATCH 15/18] ring-buffer: Consolidate add_timestamp to remove some branches

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Reorganize a little the logic to handle adding the absolute time stamp,
extended and forced time stamps, in such a way to remove a branch or two.
This is just a micro optimization.

Also add before and after time stamps to the rb_event_info structure to
display those values in the rb_check_timestamps() code, if something were to
go wrong.

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 139 +++++++++++++++++++------------------
 1 file changed, 73 insertions(+), 66 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 888bc9177937..ce125cbe98a5 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -416,6 +416,8 @@ struct rb_irq_work {
 struct rb_event_info {
 	u64			ts;
 	u64			delta;
+	u64			before;
+	u64			after;
 	unsigned long		length;
 	struct buffer_page	*tail_page;
 	int			add_timestamp;
@@ -2619,6 +2621,33 @@ rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
 static inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
 				     struct ring_buffer_event *event);
 
+#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+static inline bool sched_clock_stable(void)
+{
+	return true;
+}
+#endif
+
+static noinline void
+rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
+		   struct rb_event_info *info)
+{
+	u64 write_stamp;
+
+	WARN_ONCE(info->delta > (1ULL << 59),
+		  KERN_WARNING "Delta way too big! %llu ts=%llu before=%llu after=%llu write stamp=%llu\n%s",
+		  (unsigned long long)info->delta,
+		  (unsigned long long)info->ts,
+		  (unsigned long long)info->before,
+		  (unsigned long long)info->after,
+		  (unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
+		  sched_clock_stable() ? "" :
+		  "If you just came from a suspend/resume,\n"
+		  "please switch to the trace global clock:\n"
+		  "  echo global > /sys/kernel/debug/tracing/trace_clock\n"
+		  "or add trace_clock=global to the kernel command line\n");
+}
+
 /**
  * rb_update_event - update event type and data
  * @cpu_buffer: The per cpu buffer of the @event
@@ -2646,6 +2675,7 @@ rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
 		bool abs = info->add_timestamp &
 			(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
 
+		rb_check_timestamp(cpu_buffer, info);
 		event = rb_add_time_stamp(event, abs ? info->delta : delta, abs);
 		length -= RB_LEN_TIME_EXTEND;
 		delta = 0;
@@ -2692,13 +2722,6 @@ static unsigned rb_calculate_event_length(unsigned length)
 	return length;
 }
 
-#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
-static inline bool sched_clock_stable(void)
-{
-	return true;
-}
-#endif
-
 static __always_inline bool
 rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
 		   struct ring_buffer_event *event)
@@ -3092,24 +3115,6 @@ int ring_buffer_unlock_commit(struct trace_buffer *buffer,
 }
 EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
 
-static noinline void
-rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
-		   struct rb_event_info *info)
-{
-	u64 write_stamp;
-
-	WARN_ONCE(info->delta > (1ULL << 59),
-		  KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
-		  (unsigned long long)info->delta,
-		  (unsigned long long)info->ts,
-		  (unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
-		  sched_clock_stable() ? "" :
-		  "If you just came from a suspend/resume,\n"
-		  "please switch to the trace global clock:\n"
-		  "  echo global > /sys/kernel/debug/tracing/trace_clock\n"
-		  "or add trace_clock=global to the kernel command line\n");
-}
-
 static struct ring_buffer_event *
 __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		  struct rb_event_info *info)
@@ -3117,7 +3122,6 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	struct ring_buffer_event *event;
 	struct buffer_page *tail_page;
 	unsigned long tail, write, w;
-	u64 before, after;
 	bool a_ok;
 	bool b_ok;
 
@@ -3126,40 +3130,31 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 
  /*A*/	w = local_read(&tail_page->write) & RB_WRITE_MASK;
 	barrier();
-	b_ok = rb_time_read(&cpu_buffer->before_stamp, &before);
-	a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+	b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
+	a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
 	barrier();
 	info->ts = rb_time_stamp(cpu_buffer->buffer);
 
-	if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
+	if ((info->add_timestamp & RB_ADD_STAMP_ABSOLUTE)) {
 		info->delta = info->ts;
-		info->add_timestamp = RB_ADD_STAMP_ABSOLUTE;
 	} else {
-		info->delta = info->ts - after;
-	}
-
-	if (likely(a_ok && b_ok)) {
-		if (unlikely(test_time_stamp(info->delta))) {
-			rb_check_timestamp(cpu_buffer, info);
-			info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+		/*
+		 * If interrupting an event time update, we may need an
+		 * absolute timestamp.
+		 * Don't bother if this is the start of a new page (w == 0).
+		 */
+		if (unlikely(!a_ok || !b_ok || (info->before != info->after && w))) {
+			info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
+			info->length += RB_LEN_TIME_EXTEND;
+		} else {
+			info->delta = info->ts - info->after;
+			if (unlikely(test_time_stamp(info->delta))) {
+				info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+				info->length += RB_LEN_TIME_EXTEND;
+			}
 		}
 	}
 
-	/*
-	 * If interrupting an event time update, we may need an absolute timestamp.
-	 * Don't bother if this is the start of a new page (w == 0).
-	 */
-	if (unlikely(!a_ok || !b_ok || (before != after && w)))
-		info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
-
-	/*
-	 * If the time delta since the last event is too big to
-	 * hold in the time field of the event, then we append a
-	 * TIME EXTEND event ahead of the data event.
-	 */
-	if (unlikely(info->add_timestamp))
-		info->length += RB_LEN_TIME_EXTEND;
-
  /*B*/	rb_time_set(&cpu_buffer->before_stamp, info->ts);
 
  /*C*/	write = local_add_return(info->length, &tail_page->write);
@@ -3173,10 +3168,11 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	if (unlikely(write > BUF_PAGE_SIZE)) {
 		if (tail != w) {
 			/* before and after may now different, fix it up*/
-			b_ok = rb_time_read(&cpu_buffer->before_stamp, &before);
-			a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
-			if (a_ok && b_ok && before != after)
-				(void)rb_time_cmpxchg(&cpu_buffer->before_stamp, before, after);
+			b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
+			a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
+			if (a_ok && b_ok && info->before != info->after)
+				(void)rb_time_cmpxchg(&cpu_buffer->before_stamp,
+						      info->before, info->after);
 		}
 		return rb_move_tail(cpu_buffer, tail, info);
 	}
@@ -3193,7 +3189,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		if (likely(!(info->add_timestamp &
 			     (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
 			/* This did not interrupt any time update */
-			info->delta = info->ts - after;
+			info->delta = info->ts - info->after;
 		else
 			/* Just use full timestamp for inerrupting event */
 			info->delta = info->ts;
@@ -3201,31 +3197,33 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		if (unlikely(info->ts != save_before)) {
 			/* SLOW PATH - Interrupted between C and E */
 
-			a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+			a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
 			RB_WARN_ON(cpu_buffer, !a_ok);
 
 			/* Write stamp must only go forward */
-			if (save_before > after) {
+			if (save_before > info->after) {
 				/*
 				 * We do not care about the result, only that
 				 * it gets updated atomically.
 				 */
-				(void)rb_time_cmpxchg(&cpu_buffer->write_stamp, after, save_before);
+				(void)rb_time_cmpxchg(&cpu_buffer->write_stamp,
+						      info->after, save_before);
 			}
 		}
 	} else {
 		u64 ts;
 		/* SLOW PATH - Interrupted between A and C */
-		a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+		a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
 		/* Was interrupted before here, write_stamp must be valid */
 		RB_WARN_ON(cpu_buffer, !a_ok);
 		ts = rb_time_stamp(cpu_buffer->buffer);
 		barrier();
  /*E*/		if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
-		    after < ts) {
+		    info->after < ts) {
 			/* Nothing came after this event between C and E */
-			info->delta = ts - after;
-			(void)rb_time_cmpxchg(&cpu_buffer->write_stamp, after, info->ts);
+			info->delta = ts - info->after;
+			(void)rb_time_cmpxchg(&cpu_buffer->write_stamp,
+					      info->after, info->ts);
 			info->ts = ts;
 		} else {
 			/*
@@ -3277,6 +3275,7 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 	struct ring_buffer_event *event;
 	struct rb_event_info info;
 	int nr_loops = 0;
+	int add_ts_default;
 
 	rb_start_commit(cpu_buffer);
 	/* The commit page can not change after this */
@@ -3297,8 +3296,16 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 #endif
 
 	info.length = rb_calculate_event_length(length);
+
+	if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
+		add_ts_default = RB_ADD_STAMP_ABSOLUTE;
+		info.length += RB_LEN_TIME_EXTEND;
+	} else {
+		add_ts_default = RB_ADD_STAMP_NONE;
+	}
+
  again:
-	info.add_timestamp = RB_ADD_STAMP_NONE;
+	info.add_timestamp = add_ts_default;
 	info.delta = 0;
 
 	/*
@@ -3316,7 +3323,7 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 	event = __rb_reserve_next(cpu_buffer, &info);
 
 	if (unlikely(PTR_ERR(event) == -EAGAIN)) {
-		if (info.add_timestamp)
+		if (info.add_timestamp & (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND))
 			info.length -= RB_LEN_TIME_EXTEND;
 		goto again;
 	}
-- 
2.26.2

[for-next][PATCH 16/18] ring-buffer: Move the add_timestamp into its own function

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Make a helper function rb_add_timestamp() that moves the adding of the
extended time stamps into its own function. Also, remove the noinline and
inline for the functions it calls, as recent benchmarks appear they do not
make a difference (just let gcc decide).

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ce125cbe98a5..a30ca7ec2200 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2596,8 +2596,8 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
 	return NULL;
 }
 
-/* Slow path, do not inline */
-static noinline struct ring_buffer_event *
+/* Slow path */
+static struct ring_buffer_event *
 rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
 {
 	if (abs)
@@ -2628,7 +2628,7 @@ static inline bool sched_clock_stable(void)
 }
 #endif
 
-static noinline void
+static void
 rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 		   struct rb_event_info *info)
 {
@@ -2648,6 +2648,21 @@ rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 		  "or add trace_clock=global to the kernel command line\n");
 }
 
+static void rb_add_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
+				      struct ring_buffer_event **event,
+				      struct rb_event_info *info,
+				      u64 *delta,
+				      unsigned int *length)
+{
+	bool abs = info->add_timestamp &
+		(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
+
+	rb_check_timestamp(cpu_buffer, info);
+	*event = rb_add_time_stamp(*event, info->delta, abs);
+	*length -= RB_LEN_TIME_EXTEND;
+	*delta = 0;
+}
+
 /**
  * rb_update_event - update event type and data
  * @cpu_buffer: The per cpu buffer of the @event
@@ -2671,15 +2686,8 @@ rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
 	 * If we need to add a timestamp, then we
 	 * add it to the start of the reserved space.
 	 */
-	if (unlikely(info->add_timestamp)) {
-		bool abs = info->add_timestamp &
-			(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
-
-		rb_check_timestamp(cpu_buffer, info);
-		event = rb_add_time_stamp(event, abs ? info->delta : delta, abs);
-		length -= RB_LEN_TIME_EXTEND;
-		delta = 0;
-	}
+	if (unlikely(info->add_timestamp))
+		rb_add_timestamp(cpu_buffer, &event, info, &delta, &length);
 
 	event->time_delta = delta;
 	length -= RB_EVNT_HDR_SIZE;
-- 
2.26.2

[for-next][PATCH 17/18] ring-buffer: Call trace_clock_local() directly for RETPOLINE kernels

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

After doing some benchmarks and examining the code, I found that the ring
buffer clock calls were quite expensive, and noticed that it uses
retpolines. This is because the ring buffer clock is programmable, and can
be set. But in most cases it simply uses the fastest ns unit clock which is
the trace_clock_local(). For RETPOLINE builds, checking if the ring buffer
clock is set to trace_clock_local() and then calling it directly has brought
the time of an event on my i7 box from an average of 93 nanoseconds an event
down to 83 nanoseconds an event, and the minimum time from 81 nanoseconds to
68 nanoseconds!

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a30ca7ec2200..2bb96ee80120 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -970,8 +970,16 @@ __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
 
 static inline u64 rb_time_stamp(struct trace_buffer *buffer)
 {
+	u64 ts;
+
+	/* Skip retpolines :-( */
+	if (IS_ENABLED(CONFIG_RETPOLINE) && likely(buffer->clock == trace_clock_local))
+		ts = trace_clock_local();
+	else
+		ts = buffer->clock();
+
 	/* shift to debug/test normalization and TIME_EXTENTS */
-	return buffer->clock() << DEBUG_SHIFT;
+	return ts << DEBUG_SHIFT;
 }
 
 u64 ring_buffer_time_stamp(struct trace_buffer *buffer, int cpu)
-- 
2.26.2

[for-next][PATCH 18/18] ring-buffer: Do not trigger a WARN if clock going backwards is detected

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

After tweaking the ring buffer to be a bit faster, a warning is triggering
on one of my machines, and causing my tests to fail. This warning is caused
when the delta (current time stamp minus previous time stamp), is larger
than the max time held by the ring buffer (59 bits).

If the clock were to go backwards slightly, this would then easily trigger
this warning. The machine that it triggered on, the clock did go backwards
by around 450 nanoseconds, and this happened after a recalibration of the
TSC clock. Now that the ring buffer is faster, it detects this, and the
delta that is used larger than the max, the warning is triggered and my test
fails.

To handle the clock going backwards, look at the saved before and after time
stamps. If they are the same, it means that the current event did not
interrupt another event, and that those timestamp are of a previous event
that was recorded. If the max delta is triggered, look at those time stamps,
make sure they are the same, then use them to compare with the current
timestamp. If the current timestamp is less than the before/after time
stamps, then that means the clock being used went backward.

Print out a message that this has happened, but do not warn about it (and
only print the message once).

Still do the warning if the delta is indeed larger than what can be used.

Also remove the unneeded KERN_WARNING from the WARN_ONCE() print.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2bb96ee80120..c3a2e7509527 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2642,8 +2642,7 @@ rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 {
 	u64 write_stamp;
 
-	WARN_ONCE(info->delta > (1ULL << 59),
-		  KERN_WARNING "Delta way too big! %llu ts=%llu before=%llu after=%llu write stamp=%llu\n%s",
+	WARN_ONCE(1, "Delta way too big! %llu ts=%llu before=%llu after=%llu write stamp=%llu\n%s",
 		  (unsigned long long)info->delta,
 		  (unsigned long long)info->ts,
 		  (unsigned long long)info->before,
@@ -2665,7 +2664,26 @@ static void rb_add_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
 	bool abs = info->add_timestamp &
 		(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
 
-	rb_check_timestamp(cpu_buffer, info);
+	if (unlikely(info->delta > (1ULL << 59))) {
+		/* did the clock go backwards */
+		if (info->before == info->after && info->before > info->ts) {
+			/* not interrupted */
+			static int once;
+
+			/*
+			 * This is possible with a recalibrating of the TSC.
+			 * Do not produce a call stack, but just report it.
+			 */
+			if (!once) {
+				once++;
+				pr_warn("Ring buffer clock went backwards: %llu -> %llu\n",
+					info->before, info->ts);
+			}
+		} else
+			rb_check_timestamp(cpu_buffer, info);
+		if (!abs)
+			info->delta = 0;
+	}
 	*event = rb_add_time_stamp(*event, info->delta, abs);
 	*length -= RB_LEN_TIME_EXTEND;
 	*delta = 0;
-- 
2.26.2