[for-next][PATCH 0/7] tracing: [4.12] Allow function tracing to start earlier in boot up

[for-next][PATCH 0/7] tracing: [4.12] Allow function tracing to start earlier in boot up

[Steven Rostedt]

I've had people ask about moving tracing up further in the boot process.
This patch series looks at function tracing only. It allows for tracing
(and function filtering) to be moved right after memory is initialized.
To have it happen before memory initialization would require a bit more
work with allocating the ring buffer. But this is a start.

I placed a hook into free_reserved_area() which is used by all archs
to free the init memory. Having it pass the range being freed to ftrace
lets ftrace clean up any function that is registered such that it doesn't
try to modify code that no longer exists. 

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

Head SHA1: 2b87965a1e6b6051435315d3f04627a5dbad979c


Steven Rostedt (VMware) (7):
      tracing: Split tracing initialization into two for early initialization
      ftrace: Move ftrace_init() to right after memory initialization
      tracing: Postpone tracer start-up tests till the system is more robust
      ftrace: Have function tracing start in early boot up
      ftrace: Allow for function tracing to record init functions on boot up
      tracing: Move trace_handle_return() out of line
      ftrace/x86: Do no run CPU sync when there is only one CPU online

----
 arch/x86/kernel/ftrace.c       |  8 +++-
 include/linux/ftrace.h         |  7 ++++
 include/linux/init.h           |  4 +-
 include/linux/trace_events.h   | 11 +----
 init/main.c                    |  9 +++--
 kernel/trace/ftrace.c          | 44 ++++++++++++++++++++
 kernel/trace/trace.c           | 92 +++++++++++++++++++++++++++++++++++++++++-
 kernel/trace/trace.h           |  2 +
 kernel/trace/trace_functions.c |  3 +-
 mm/page_alloc.c                |  4 ++
 scripts/recordmcount.c         |  1 +
 scripts/recordmcount.pl        |  1 +
 12 files changed, 168 insertions(+), 18 deletions(-)

[for-next][PATCH 1/7] tracing: Split tracing initialization into two for early initialization

[Steven Rostedt]

[-- Attachment #1: 0001-tracing-Split-tracing-initialization-into-two-for-ea.patch --]
[-- Type: text/plain, Size: 2131 bytes --]

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

Create an early_trace_init() function that will initialize the buffers and
allow for ealier use of trace_printk(). This will also allow for future work
to have function tracing start earlier at boot up.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/ftrace.h | 2 ++
 init/main.c            | 5 ++++-
 kernel/trace/trace.c   | 6 +++++-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 3633e8beff39..569db5589851 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -42,8 +42,10 @@
 /* Main tracing buffer and events set up */
 #ifdef CONFIG_TRACING
 void trace_init(void);
+void early_trace_init(void);
 #else
 static inline void trace_init(void) { }
+static inline void early_trace_init(void) { }
 #endif
 
 struct module;
diff --git a/init/main.c b/init/main.c
index f9c9d9948203..81a49e8d54cc 100644
--- a/init/main.c
+++ b/init/main.c
@@ -545,6 +545,9 @@ asmlinkage __visible void __init start_kernel(void)
 	trap_init();
 	mm_init();
 
+	/* trace_printk can be enabled here */
+	early_trace_init();
+
 	/*
 	 * Set up the scheduler prior starting any interrupts (such as the
 	 * timer interrupt). Full topology setup happens at smp_init()
@@ -570,7 +573,7 @@ asmlinkage __visible void __init start_kernel(void)
 
 	rcu_init();
 
-	/* trace_printk() and trace points may be used after this */
+	/* Trace events are available after this */
 	trace_init();
 
 	context_tracking_init();
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f35109514a01..6757561d9617 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7999,7 +7999,7 @@ __init static int tracer_alloc_buffers(void)
 	return ret;
 }
 
-void __init trace_init(void)
+void __init early_trace_init(void)
 {
 	if (tracepoint_printk) {
 		tracepoint_print_iter =
@@ -8010,6 +8010,10 @@ void __init trace_init(void)
 			static_key_enable(&tracepoint_printk_key.key);
 	}
 	tracer_alloc_buffers();
+}
+
+void __init trace_init(void)
+{
 	trace_event_init();
 }
 
-- 
2.10.2

[for-next][PATCH 2/7] ftrace: Move ftrace_init() to right after memory initialization

[Steven Rostedt]

[-- Attachment #1: 0002-ftrace-Move-ftrace_init-to-right-after-memory-initia.patch --]
[-- Type: text/plain, Size: 927 bytes --]

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

Initialize the ftrace records immediately after memory initialization, as
that is all that is required for the records to be created. This will allow
for future work to get function tracing started earlier in the boot process.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 init/main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/init/main.c b/init/main.c
index 81a49e8d54cc..c0137b916aa1 100644
--- a/init/main.c
+++ b/init/main.c
@@ -545,6 +545,8 @@ asmlinkage __visible void __init start_kernel(void)
 	trap_init();
 	mm_init();
 
+	ftrace_init();
+
 	/* trace_printk can be enabled here */
 	early_trace_init();
 
@@ -673,8 +675,6 @@ asmlinkage __visible void __init start_kernel(void)
 		efi_free_boot_services();
 	}
 
-	ftrace_init();
-
 	/* Do the rest non-__init'ed, we're now alive */
 	rest_init();
 }
-- 
2.10.2

[for-next][PATCH 3/7] tracing: Postpone tracer start-up tests till the system is more robust

[Steven Rostedt]

[-- Attachment #1: 0003-tracing-Postpone-tracer-start-up-tests-till-the-syst.patch --]
[-- Type: text/plain, Size: 2964 bytes --]

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

As tracing can now be enabled very early in boot up, even before some
critical system services (like scheduling), do not run the tracer selftests
until after early_initcall() is performed. If a tracer is registered before
such time, it is saved off in a list and the test is run when the system is
able to handle more diverse functions.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6757561d9617..68a6f78f6862 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1424,6 +1424,28 @@ static int wait_on_pipe(struct trace_iterator *iter, bool full)
 }
 
 #ifdef CONFIG_FTRACE_STARTUP_TEST
+static bool selftests_can_run;
+
+struct trace_selftests {
+	struct list_head		list;
+	struct tracer			*type;
+};
+
+static LIST_HEAD(postponed_selftests);
+
+static int save_selftest(struct tracer *type)
+{
+	struct trace_selftests *selftest;
+
+	selftest = kmalloc(sizeof(*selftest), GFP_KERNEL);
+	if (!selftest)
+		return -ENOMEM;
+
+	selftest->type = type;
+	list_add(&selftest->list, &postponed_selftests);
+	return 0;
+}
+
 static int run_tracer_selftest(struct tracer *type)
 {
 	struct trace_array *tr = &global_trace;
@@ -1434,6 +1456,14 @@ static int run_tracer_selftest(struct tracer *type)
 		return 0;
 
 	/*
+	 * If a tracer registers early in boot up (before scheduling is
+	 * initialized and such), then do not run its selftests yet.
+	 * Instead, run it a little later in the boot process.
+	 */
+	if (!selftests_can_run)
+		return save_selftest(type);
+
+	/*
 	 * Run a selftest on this tracer.
 	 * Here we reset the trace buffer, and set the current
 	 * tracer to be this tracer. The tracer can then run some
@@ -1482,6 +1512,47 @@ static int run_tracer_selftest(struct tracer *type)
 	printk(KERN_CONT "PASSED\n");
 	return 0;
 }
+
+static __init int init_trace_selftests(void)
+{
+	struct trace_selftests *p, *n;
+	struct tracer *t, **last;
+	int ret;
+
+	selftests_can_run = true;
+
+	mutex_lock(&trace_types_lock);
+
+	if (list_empty(&postponed_selftests))
+		goto out;
+
+	pr_info("Running postponed tracer tests:\n");
+
+	list_for_each_entry_safe(p, n, &postponed_selftests, list) {
+		ret = run_tracer_selftest(p->type);
+		/* If the test fails, then warn and remove from available_tracers */
+		if (ret < 0) {
+			WARN(1, "tracer: %s failed selftest, disabling\n",
+			     p->type->name);
+			last = &trace_types;
+			for (t = trace_types; t; t = t->next) {
+				if (t == p->type) {
+					*last = t->next;
+					break;
+				}
+				last = &t->next;
+			}
+		}
+		list_del(&p->list);
+		kfree(p);
+	}
+
+ out:
+	mutex_unlock(&trace_types_lock);
+
+	return 0;
+}
+early_initcall(init_trace_selftests);
 #else
 static inline int run_tracer_selftest(struct tracer *type)
 {
-- 
2.10.2

[for-next][PATCH 4/7] ftrace: Have function tracing start in early boot up

[Steven Rostedt]

[-- Attachment #1: 0004-ftrace-Have-function-tracing-start-in-early-boot-up.patch --]
[-- Type: text/plain, Size: 2433 bytes --]

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

Register the function tracer right after the tracing buffers are initialized
in early boot up. This will allow function tracing to begin early if it is
enabled via the kernel command line.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace.c           | 3 +++
 kernel/trace/trace.h           | 2 ++
 kernel/trace/trace_functions.c | 3 +--
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 68a6f78f6862..4fa8e8f3c765 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8036,6 +8036,9 @@ __init static int tracer_alloc_buffers(void)
 
 	register_tracer(&nop_trace);
 
+	/* Function tracing may start here (via kernel command line) */
+	init_function_trace();
+
 	/* All seems OK, enable tracing */
 	tracing_disabled = 0;
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index ae1cce91fead..571acee52a32 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -896,6 +896,7 @@ int using_ftrace_ops_list_func(void);
 void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d_tracer);
 void ftrace_init_tracefs_toplevel(struct trace_array *tr,
 				  struct dentry *d_tracer);
+int init_function_trace(void);
 #else
 static inline int ftrace_trace_task(struct trace_array *tr)
 {
@@ -914,6 +915,7 @@ ftrace_init_global_array_ops(struct trace_array *tr) { }
 static inline void ftrace_reset_array_ops(struct trace_array *tr) { }
 static inline void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d) { }
 static inline void ftrace_init_tracefs_toplevel(struct trace_array *tr, struct dentry *d) { }
+static inline int init_function_trace(void) { return 0; }
 /* ftace_func_t type is not defined, use macro instead of static inline */
 #define ftrace_init_array_ops(tr, func) do { } while (0)
 #endif /* CONFIG_FUNCTION_TRACER */
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 0efa00d80623..4199ca61b0e5 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -687,9 +687,8 @@ static inline int init_func_cmd_traceon(void)
 }
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
-static __init int init_function_trace(void)
+__init int init_function_trace(void)
 {
 	init_func_cmd_traceon();
 	return register_tracer(&function_trace);
 }
-core_initcall(init_function_trace);
-- 
2.10.2

[for-next][PATCH 5/7] ftrace: Allow for function tracing to record init functions on boot up

[Steven Rostedt]

[-- Attachment #1: 0005-ftrace-Allow-for-function-tracing-to-record-init-fun.patch --]
[-- Type: text/plain, Size: 5726 bytes --]

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

Adding a hook into free_reserve_area() that informs ftrace that boot up init
text is being free, lets ftrace safely remove those init functions from its
records, which keeps ftrace from trying to modify text that no longer
exists.

Note, this still does not allow for tracing .init text of modules, as
modules require different work for freeing its init code.

Link: http://lkml.kernel.org/r/1488502497.7212.24.camel@linux.intel.com

Cc: linux-mm@kvack.org
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Requested-by: Todd Brandt <todd.e.brandt@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/ftrace.h  |  5 +++++
 include/linux/init.h    |  4 +++-
 kernel/trace/ftrace.c   | 44 ++++++++++++++++++++++++++++++++++++++++++++
 mm/page_alloc.c         |  4 ++++
 scripts/recordmcount.c  |  1 +
 scripts/recordmcount.pl |  1 +
 6 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 569db5589851..0276a2c487e6 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -146,6 +146,10 @@ struct ftrace_ops_hash {
 	struct ftrace_hash		*filter_hash;
 	struct mutex			regex_lock;
 };
+
+void ftrace_free_mem(void *start, void *end);
+#else
+static inline void ftrace_free_mem(void *start, void *end) { }
 #endif
 
 /*
@@ -262,6 +266,7 @@ static inline int ftrace_nr_registered_ops(void)
 }
 static inline void clear_ftrace_function(void) { }
 static inline void ftrace_kill(void) { }
+static inline void ftrace_free_mem(void *start, void *end) { }
 #endif /* CONFIG_FUNCTION_TRACER */
 
 #ifdef CONFIG_STACK_TRACER
diff --git a/include/linux/init.h b/include/linux/init.h
index 79af0962fd52..94769d687cf0 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -39,7 +39,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold notrace __latent_entropy
+#define __init		__section(.init.text) __cold __inittrace __latent_entropy
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)
@@ -68,8 +68,10 @@
 
 #ifdef MODULE
 #define __exitused
+#define __inittrace notrace
 #else
 #define __exitused  __used
+#define __inittrace
 #endif
 
 #define __exit          __section(.exit.text) __exitused __cold notrace
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b9691ee8f6c1..0556a202c055 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5262,6 +5262,50 @@ void ftrace_module_init(struct module *mod)
 }
 #endif /* CONFIG_MODULES */
 
+void ftrace_free_mem(void *start_ptr, void *end_ptr)
+{
+	unsigned long start = (unsigned long)start_ptr;
+	unsigned long end = (unsigned long)end_ptr;
+	struct ftrace_page **last_pg = &ftrace_pages_start;
+	struct ftrace_page *pg;
+	struct dyn_ftrace *rec;
+	struct dyn_ftrace key;
+	int order;
+
+	key.ip = start;
+	key.flags = end;	/* overload flags, as it is unsigned long */
+
+	mutex_lock(&ftrace_lock);
+
+	for (pg = ftrace_pages_start; pg; last_pg = &pg->next, pg = *last_pg) {
+		if (end < pg->records[0].ip ||
+		    start >= (pg->records[pg->index - 1].ip + MCOUNT_INSN_SIZE))
+			continue;
+ again:
+		rec = bsearch(&key, pg->records, pg->index,
+			      sizeof(struct dyn_ftrace),
+			      ftrace_cmp_recs);
+		if (!rec)
+			continue;
+		pg->index--;
+		if (!pg->index) {
+			*last_pg = pg->next;
+			order = get_count_order(pg->size / ENTRIES_PER_PAGE);
+			free_pages((unsigned long)pg->records, order);
+			kfree(pg);
+			pg = container_of(last_pg, struct ftrace_page, next);
+			if (!(*last_pg))
+				ftrace_pages = pg;
+			continue;
+		}
+		memmove(rec, rec + 1,
+			(pg->index - (rec - pg->records)) * sizeof(*rec));
+		/* More than one function may be in this block */
+		goto again;
+	}
+	mutex_unlock(&ftrace_lock);
+}
+
 void __init ftrace_init(void)
 {
 	extern unsigned long __start_mcount_loc[];
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6cbde310abed..eee82bfb7cd8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -65,6 +65,7 @@
 #include <linux/page_owner.h>
 #include <linux/kthread.h>
 #include <linux/memcontrol.h>
+#include <linux/ftrace.h>
 
 #include <asm/sections.h>
 #include <asm/tlbflush.h>
@@ -6605,6 +6606,9 @@ unsigned long free_reserved_area(void *start, void *end, int poison, char *s)
 	void *pos;
 	unsigned long pages = 0;
 
+	/* This may be .init text, inform ftrace to remove it */
+	ftrace_free_mem(start, end);
+
 	start = (void *)PAGE_ALIGN((unsigned long)start);
 	end = (void *)((unsigned long)end & PAGE_MASK);
 	for (pos = start; pos < end; pos += PAGE_SIZE, pages++) {
diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index aeb34223167c..16e086dcc567 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -412,6 +412,7 @@ static int
 is_mcounted_section_name(char const *const txtname)
 {
 	return strcmp(".text",           txtname) == 0 ||
+		strcmp(".init.text",     txtname) == 0 ||
 		strcmp(".ref.text",      txtname) == 0 ||
 		strcmp(".sched.text",    txtname) == 0 ||
 		strcmp(".spinlock.text", txtname) == 0 ||
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 0b6002b36f20..1633c3e6c0b9 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -130,6 +130,7 @@ if ($inputfile =~ m,kernel/trace/ftrace\.o$,) {
 # Acceptable sections to record.
 my %text_sections = (
      ".text" => 1,
+     ".init.text" => 1,
      ".ref.text" => 1,
      ".sched.text" => 1,
      ".spinlock.text" => 1,
-- 
2.10.2

[for-next][PATCH 6/7] tracing: Move trace_handle_return() out of line

[Steven Rostedt]

[-- Attachment #1: 0006-tracing-Move-trace_handle_return-out-of-line.patch --]
[-- Type: text/plain, Size: 6189 bytes --]

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

Currently trace_handle_return() looks like this:

 static inline enum print_line_t trace_handle_return(struct trace_seq *s)
 {
        return trace_seq_has_overflowed(s) ?
                TRACE_TYPE_PARTIAL_LINE : TRACE_TYPE_HANDLED;
 }

Where trace_seq_overflowed(s) is:

 static inline bool trace_seq_has_overflowed(struct trace_seq *s)
 {
	return s->full || seq_buf_has_overflowed(&s->seq);
 }

And seq_buf_has_overflowed(&s->seq) is:

 static inline bool
 seq_buf_has_overflowed(struct seq_buf *s)
 {
	return s->len > s->size;
 }

Making trace_handle_return() into:

 return (s->full || (s->seq->len > s->seq->size)) ?
           TRACE_TYPE_PARTIAL_LINE :
           TRACE_TYPE_HANDLED;

One would think this is not an issue to keep as an inline. But because this
is used in the TRACE_EVENT() macro, it is extended for every tracepoint in
the system. Taking a look at a single tracepoint x86_irq_vector (was the
first one I randomly chosen). As trace_handle_return is used in the
TRACE_EVENT() macro of trace_raw_output_##call() we disassemble
trace_raw_output_x86_irq_vector and do a diff:

- is the original
+ is the out-of-line code

I removed identical lines that were different just due to different
addresses.

--- /tmp/irq-vec-orig	2017-03-16 09:12:48.569384851 -0400
+++ /tmp/irq-vec-ool	2017-03-16 09:13:39.378153385 -0400
@@ -6,27 +6,23 @@
        53                      push   %rbx
        48 89 fb                mov    %rdi,%rbx
        4c 8b a7 c0 20 00 00    mov    0x20c0(%rdi),%r12
        e8 f7 72 13 00          callq  ffffffff81155c80 <trace_raw_output_prep>
        83 f8 01                cmp    $0x1,%eax
        74 05                   je     ffffffff8101e993 <trace_raw_output_x86_irq_vector+0x23>
        5b                      pop    %rbx
        41 5c                   pop    %r12
        5d                      pop    %rbp
        c3                      retq
        41 8b 54 24 08          mov    0x8(%r12),%edx
-       48 8d bb 98 10 00 00    lea    0x1098(%rbx),%rdi
+       48 81 c3 98 10 00 00    add    $0x1098,%rbx
-       48 c7 c6 7b 8a a0 81    mov    $0xffffffff81a08a7b,%rsi
+       48 c7 c6 ab 8a a0 81    mov    $0xffffffff81a08aab,%rsi
-       e8 c5 85 13 00          callq  ffffffff81156f70 <trace_seq_printf>

 === here's the start of the main difference ===

+       48 89 df                mov    %rbx,%rdi
+       e8 62 7e 13 00          callq  ffffffff81156810 <trace_seq_printf>
-       8b 93 b8 20 00 00       mov    0x20b8(%rbx),%edx
-       31 c0                   xor    %eax,%eax
-       85 d2                   test   %edx,%edx
-       75 11                   jne    ffffffff8101e9c8 <trace_raw_output_x86_irq_vector+0x58>
-       48 8b 83 a8 20 00 00    mov    0x20a8(%rbx),%rax
-       48 39 83 a0 20 00 00    cmp    %rax,0x20a0(%rbx)
-       0f 93 c0                setae  %al
+       48 89 df                mov    %rbx,%rdi
+       e8 4a c5 12 00          callq  ffffffff8114af00 <trace_handle_return>
        5b                      pop    %rbx
-       0f b6 c0                movzbl %al,%eax

 === end ===

        41 5c                   pop    %r12
        5d                      pop    %rbp
        c3                      retq

If you notice, the original has 22 bytes of text more than the out of line
version. As this is for every TRACE_EVENT() defined in the system, this can
become quite large.

   text	   data	    bss	    dec	    hex	filename
8690305	5450490	1298432	15439227	 eb957b	vmlinux-orig
8681725	5450490	1298432	15430647	 eb73f7	vmlinux-handle

This change has a total of 8580 bytes in savings.

 $ objdump -dr /tmp/vmlinux-orig | grep '^[0-9a-f]* <trace_raw_output' | wc -l
324

That's 324 tracepoints. But this does not include modules (which contain
many more tracepoints). For an allyesconfig build:

 $ objdump -dr vmlinux-allyes-orig | grep '^[0-9a-f]* <trace_raw_output' | wc -l
1401

That's 1401 tracepoints giving us:

   text    data     bss     dec     hex filename
137920629       140221067       53264384        331406080       13c0db00 vmlinux-allyes-orig
137827709       140221067       53264384        331313160       13bf7008 vmlinux-allyes-handle

92920 bytes in savings!!!

Link: http://lkml.kernel.org/r/20170315021431.13107-2-andi@firstfloor.org

Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/trace_events.h | 11 +----------
 kernel/trace/trace.c         | 12 ++++++++++++
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 0af63c4381b9..a556805eff8a 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -138,16 +138,7 @@ enum print_line_t {
 	TRACE_TYPE_NO_CONSUME	= 3	/* Handled but ask to not consume */
 };
 
-/*
- * Several functions return TRACE_TYPE_PARTIAL_LINE if the trace_seq
- * overflowed, and TRACE_TYPE_HANDLED otherwise. This helper function
- * simplifies those functions and keeps them in sync.
- */
-static inline enum print_line_t trace_handle_return(struct trace_seq *s)
-{
-	return trace_seq_has_overflowed(s) ?
-		TRACE_TYPE_PARTIAL_LINE : TRACE_TYPE_HANDLED;
-}
+enum print_line_t trace_handle_return(struct trace_seq *s);
 
 void tracing_generic_entry_update(struct trace_entry *entry,
 				  unsigned long flags,
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4fa8e8f3c765..b5d4b80f2d45 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1998,6 +1998,18 @@ void tracing_record_cmdline(struct task_struct *tsk)
 		__this_cpu_write(trace_cmdline_save, false);
 }
 
+/*
+ * Several functions return TRACE_TYPE_PARTIAL_LINE if the trace_seq
+ * overflowed, and TRACE_TYPE_HANDLED otherwise. This helper function
+ * simplifies those functions and keeps them in sync.
+ */
+enum print_line_t trace_handle_return(struct trace_seq *s)
+{
+	return trace_seq_has_overflowed(s) ?
+		TRACE_TYPE_PARTIAL_LINE : TRACE_TYPE_HANDLED;
+}
+EXPORT_SYMBOL_GPL(trace_handle_return);
+
 void
 tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags,
 			     int pc)
-- 
2.10.2

[for-next][PATCH 7/7] ftrace/x86: Do no run CPU sync when there is only one CPU online

[Steven Rostedt]

[-- Attachment #1: 0007-ftrace-x86-Do-no-run-CPU-sync-when-there-is-only-one.patch --]
[-- Type: text/plain, Size: 1586 bytes --]

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

Moving enabling of function tracing to early boot, even before scheduling is
enabled, means that it is not safe to enable interrupts. When function
tracing was enabled at boot up, it use to happen after scheduling and the
other CPUs were brought up. That required running a sync across all CPUs
when modifying the function hook locations in the code. To do the
synchronization, interrupts had to be enabled. Now function tracing can be
started before the other CPUs are brought up, and enabling interrupts in
that case is dangerous. As only tho boot CPU is active, there is no reason
to run the synchronization. If the online CPU count is one, do not bother
doing the synchronization. This removes the need to enable interrupts.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/x86/kernel/ftrace.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 8f3d9cf26ff9..70945fbd1258 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -533,7 +533,13 @@ static void do_sync_core(void *data)
 
 static void run_sync(void)
 {
-	int enable_irqs = irqs_disabled();
+	int enable_irqs;
+
+	/* No need to sync if there's only one CPU */
+	if (num_online_cpus() == 1)
+		return;
+
+	enable_irqs = irqs_disabled();
 
 	/* We may be called with interrupts disabled (on bootup). */
 	if (enable_irqs)
-- 
2.10.2