* [PATCH 1/3] context_tracking: remove duplicate enabled check
2015-10-28 1:39 [PATCH 0/3] context_tracking: streamline code, avoid IRQ save/restore Paolo Bonzini
@ 2015-10-28 1:39 ` Paolo Bonzini
2015-10-28 5:19 ` Andy Lutomirski
2015-11-09 13:57 ` Rik van Riel
2015-10-28 1:39 ` [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit Paolo Bonzini
` (2 subsequent siblings)
3 siblings, 2 replies; 14+ messages in thread
From: Paolo Bonzini @ 2015-10-28 1:39 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Andy Lutomirski, Frederic Weisbecker, Rik van Riel, Paul McKenney
All calls to context_tracking_enter and context_tracking_exit
are already checking context_tracking_is_enabled, except the
context_tracking_user_enter and context_tracking_user_exit
functions left in for the benefit of assembly calls.
Pull the check up to those functions, by making them simple
wrappers around the user_enter and user_exit inline functions.
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
include/linux/context_tracking.h | 4 ++--
kernel/context_tracking.c | 16 ++--------------
2 files changed, 4 insertions(+), 16 deletions(-)
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 008fc67d0d96..6ef136ff0897 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -18,13 +18,13 @@ extern void context_tracking_user_exit(void);
static inline void user_enter(void)
{
if (context_tracking_is_enabled())
- context_tracking_user_enter();
+ context_tracking_enter(CONTEXT_USER);
}
static inline void user_exit(void)
{
if (context_tracking_is_enabled())
- context_tracking_user_exit();
+ context_tracking_exit(CONTEXT_USER);
}
static inline enum ctx_state exception_enter(void)
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 0a495ab35bc7..6d4c6ce21275 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -63,15 +63,6 @@ void context_tracking_enter(enum ctx_state state)
unsigned long flags;
/*
- * Repeat the user_enter() check here because some archs may be calling
- * this from asm and if no CPU needs context tracking, they shouldn't
- * go further. Repeat the check here until they support the inline static
- * key check.
- */
- if (!context_tracking_is_enabled())
- return;
-
- /*
* Some contexts may involve an exception occuring in an irq,
* leading to that nesting:
* rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
@@ -128,7 +119,7 @@ EXPORT_SYMBOL_GPL(context_tracking_enter);
void context_tracking_user_enter(void)
{
- context_tracking_enter(CONTEXT_USER);
+ user_enter();
}
NOKPROBE_SYMBOL(context_tracking_user_enter);
@@ -148,9 +139,6 @@ void context_tracking_exit(enum ctx_state state)
{
unsigned long flags;
- if (!context_tracking_is_enabled())
- return;
-
if (in_interrupt())
return;
@@ -181,7 +169,7 @@ EXPORT_SYMBOL_GPL(context_tracking_exit);
void context_tracking_user_exit(void)
{
- context_tracking_exit(CONTEXT_USER);
+ user_exit();
}
NOKPROBE_SYMBOL(context_tracking_user_exit);
--
2.5.0
^ permalink raw reply related [flat|nested] 14+ messages in thread
* Re: [PATCH 1/3] context_tracking: remove duplicate enabled check
2015-10-28 1:39 ` [PATCH 1/3] context_tracking: remove duplicate enabled check Paolo Bonzini
@ 2015-10-28 5:19 ` Andy Lutomirski
2015-11-07 9:38 ` Paolo Bonzini
2015-11-09 13:57 ` Rik van Riel
1 sibling, 1 reply; 14+ messages in thread
From: Andy Lutomirski @ 2015-10-28 5:19 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm list, Andy Lutomirski, Frederic Weisbecker,
Rik van Riel, Paul McKenney
On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> All calls to context_tracking_enter and context_tracking_exit
> are already checking context_tracking_is_enabled, except the
> context_tracking_user_enter and context_tracking_user_exit
> functions left in for the benefit of assembly calls.
>
> Pull the check up to those functions, by making them simple
> wrappers around the user_enter and user_exit inline functions.
This makes my brain hurt. Assuming that this survives a boot with
CONFIG_CONTEXT_TRACKING_FORCE=y and CONFIG_PROVE_LOCKING=y (with the
implied CONFIG_PROVE_RCU), then:
Acked-by: Andy Lutomirski <luto@kernel.org>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH 1/3] context_tracking: remove duplicate enabled check
2015-10-28 5:19 ` Andy Lutomirski
@ 2015-11-07 9:38 ` Paolo Bonzini
0 siblings, 0 replies; 14+ messages in thread
From: Paolo Bonzini @ 2015-11-07 9:38 UTC (permalink / raw)
To: Andy Lutomirski
Cc: linux-kernel, kvm list, Andy Lutomirski, Frederic Weisbecker,
Rik van Riel, Paul McKenney
On 28/10/2015 06:19, Andy Lutomirski wrote:
> On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> All calls to context_tracking_enter and context_tracking_exit
>> are already checking context_tracking_is_enabled, except the
>> context_tracking_user_enter and context_tracking_user_exit
>> functions left in for the benefit of assembly calls.
>>
>> Pull the check up to those functions, by making them simple
>> wrappers around the user_enter and user_exit inline functions.
>
> This makes my brain hurt. Assuming that this survives a boot with
> CONFIG_CONTEXT_TRACKING_FORCE=y and CONFIG_PROVE_LOCKING=y (with the
> implied CONFIG_PROVE_RCU), then:
>
> Acked-by: Andy Lutomirski <luto@kernel.org>
Tested now.
Paolo
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH 1/3] context_tracking: remove duplicate enabled check
2015-10-28 1:39 ` [PATCH 1/3] context_tracking: remove duplicate enabled check Paolo Bonzini
2015-10-28 5:19 ` Andy Lutomirski
@ 2015-11-09 13:57 ` Rik van Riel
1 sibling, 0 replies; 14+ messages in thread
From: Rik van Riel @ 2015-11-09 13:57 UTC (permalink / raw)
To: Paolo Bonzini, linux-kernel, kvm
Cc: Andy Lutomirski, Frederic Weisbecker, Paul McKenney
On 10/27/2015 09:39 PM, Paolo Bonzini wrote:
> All calls to context_tracking_enter and context_tracking_exit
> are already checking context_tracking_is_enabled, except the
> context_tracking_user_enter and context_tracking_user_exit
> functions left in for the benefit of assembly calls.
>
> Pull the check up to those functions, by making them simple
> wrappers around the user_enter and user_exit inline functions.
>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Tested-by: Rik van Riel <riel@redhat.com>
--
All rights reversed
^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit
2015-10-28 1:39 [PATCH 0/3] context_tracking: streamline code, avoid IRQ save/restore Paolo Bonzini
2015-10-28 1:39 ` [PATCH 1/3] context_tracking: remove duplicate enabled check Paolo Bonzini
@ 2015-10-28 1:39 ` Paolo Bonzini
2015-10-28 5:20 ` Andy Lutomirski
2015-11-09 13:58 ` Rik van Riel
2015-10-28 1:39 ` [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel " Paolo Bonzini
2015-10-28 2:05 ` [PATCH 0/3] context_tracking: streamline code, avoid IRQ save/restore Paolo Bonzini
3 siblings, 2 replies; 14+ messages in thread
From: Paolo Bonzini @ 2015-10-28 1:39 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Andy Lutomirski, Frederic Weisbecker, Rik van Riel, Paul McKenney
guest_enter and guest_exit must be called with interrupts disabled,
since they take the vtime_seqlock with write_seq{lock,unlock}.
Therefore, it is not necessary to check for exceptions, nor to
save/restore the IRQ state, when context tracking functions are
called by guest_enter and guest_exit.
Split the body of context_tracking_entry and context_tracking_exit
out to __-prefixed functions, and use them from KVM.
Rik van Riel has measured this to speed up a tight vmentry/vmexit
loop by about 2%.
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
include/linux/context_tracking.h | 8 +++--
kernel/context_tracking.c | 64 ++++++++++++++++++++++++----------------
2 files changed, 44 insertions(+), 28 deletions(-)
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 6ef136ff0897..68b575afe5f5 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -10,6 +10,10 @@
#ifdef CONFIG_CONTEXT_TRACKING
extern void context_tracking_cpu_set(int cpu);
+/* Called with interrupts disabled. */
+extern void __context_tracking_enter(enum ctx_state state);
+extern void __context_tracking_exit(enum ctx_state state);
+
extern void context_tracking_enter(enum ctx_state state);
extern void context_tracking_exit(enum ctx_state state);
extern void context_tracking_user_enter(void);
@@ -88,13 +92,13 @@ static inline void guest_enter(void)
current->flags |= PF_VCPU;
if (context_tracking_is_enabled())
- context_tracking_enter(CONTEXT_GUEST);
+ __context_tracking_enter(CONTEXT_GUEST);
}
static inline void guest_exit(void)
{
if (context_tracking_is_enabled())
- context_tracking_exit(CONTEXT_GUEST);
+ __context_tracking_exit(CONTEXT_GUEST);
if (vtime_accounting_enabled())
vtime_guest_exit(current);
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 6d4c6ce21275..d8560ee3bab7 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -58,27 +58,13 @@ static void context_tracking_recursion_exit(void)
* instructions to execute won't use any RCU read side critical section
* because this function sets RCU in extended quiescent state.
*/
-void context_tracking_enter(enum ctx_state state)
+void __context_tracking_enter(enum ctx_state state)
{
- unsigned long flags;
-
- /*
- * Some contexts may involve an exception occuring in an irq,
- * leading to that nesting:
- * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
- * This would mess up the dyntick_nesting count though. And rcu_irq_*()
- * helpers are enough to protect RCU uses inside the exception. So
- * just return immediately if we detect we are in an IRQ.
- */
- if (in_interrupt())
- return;
-
/* Kernel threads aren't supposed to go to userspace */
WARN_ON_ONCE(!current->mm);
- local_irq_save(flags);
if (!context_tracking_recursion_enter())
- goto out_irq_restore;
+ return;
if ( __this_cpu_read(context_tracking.state) != state) {
if (__this_cpu_read(context_tracking.active)) {
@@ -111,7 +97,27 @@ void context_tracking_enter(enum ctx_state state)
__this_cpu_write(context_tracking.state, state);
}
context_tracking_recursion_exit();
-out_irq_restore:
+}
+NOKPROBE_SYMBOL(__context_tracking_enter);
+EXPORT_SYMBOL_GPL(__context_tracking_enter);
+
+void context_tracking_enter(enum ctx_state state)
+{
+ unsigned long flags;
+
+ /*
+ * Some contexts may involve an exception occuring in an irq,
+ * leading to that nesting:
+ * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
+ * This would mess up the dyntick_nesting count though. And rcu_irq_*()
+ * helpers are enough to protect RCU uses inside the exception. So
+ * just return immediately if we detect we are in an IRQ.
+ */
+ if (in_interrupt())
+ return;
+
+ local_irq_save(flags);
+ __context_tracking_enter(state);
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(context_tracking_enter);
@@ -135,16 +141,10 @@ NOKPROBE_SYMBOL(context_tracking_user_enter);
* This call supports re-entrancy. This way it can be called from any exception
* handler without needing to know if we came from userspace or not.
*/
-void context_tracking_exit(enum ctx_state state)
+void __context_tracking_exit(enum ctx_state state)
{
- unsigned long flags;
-
- if (in_interrupt())
- return;
-
- local_irq_save(flags);
if (!context_tracking_recursion_enter())
- goto out_irq_restore;
+ return;
if (__this_cpu_read(context_tracking.state) == state) {
if (__this_cpu_read(context_tracking.active)) {
@@ -161,7 +161,19 @@ void context_tracking_exit(enum ctx_state state)
__this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
}
context_tracking_recursion_exit();
-out_irq_restore:
+}
+NOKPROBE_SYMBOL(__context_tracking_exit);
+EXPORT_SYMBOL_GPL(__context_tracking_exit);
+
+void context_tracking_exit(enum ctx_state state)
+{
+ unsigned long flags;
+
+ if (in_interrupt())
+ return;
+
+ local_irq_save(flags);
+ __context_tracking_exit(state);
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(context_tracking_exit);
--
2.5.0
^ permalink raw reply related [flat|nested] 14+ messages in thread
* Re: [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit
2015-10-28 1:39 ` [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit Paolo Bonzini
@ 2015-10-28 5:20 ` Andy Lutomirski
2015-11-09 13:58 ` Rik van Riel
1 sibling, 0 replies; 14+ messages in thread
From: Andy Lutomirski @ 2015-10-28 5:20 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm list, Andy Lutomirski, Frederic Weisbecker,
Rik van Riel, Paul McKenney
On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> guest_enter and guest_exit must be called with interrupts disabled,
> since they take the vtime_seqlock with write_seq{lock,unlock}.
> Therefore, it is not necessary to check for exceptions, nor to
> save/restore the IRQ state, when context tracking functions are
> called by guest_enter and guest_exit.
>
> Split the body of context_tracking_entry and context_tracking_exit
> out to __-prefixed functions, and use them from KVM.
>
> Rik van Riel has measured this to speed up a tight vmentry/vmexit
> loop by about 2%.
Looks generally sensible. I'm not familiar enough with the code to
call it reviewed-by while sitting on the airport shuttle.
--Andy
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit
2015-10-28 1:39 ` [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit Paolo Bonzini
2015-10-28 5:20 ` Andy Lutomirski
@ 2015-11-09 13:58 ` Rik van Riel
1 sibling, 0 replies; 14+ messages in thread
From: Rik van Riel @ 2015-11-09 13:58 UTC (permalink / raw)
To: Paolo Bonzini, linux-kernel, kvm
Cc: Andy Lutomirski, Frederic Weisbecker, Paul McKenney
On 10/27/2015 09:39 PM, Paolo Bonzini wrote:
> guest_enter and guest_exit must be called with interrupts disabled,
> since they take the vtime_seqlock with write_seq{lock,unlock}.
> Therefore, it is not necessary to check for exceptions, nor to
> save/restore the IRQ state, when context tracking functions are
> called by guest_enter and guest_exit.
>
> Split the body of context_tracking_entry and context_tracking_exit
> out to __-prefixed functions, and use them from KVM.
>
> Rik van Riel has measured this to speed up a tight vmentry/vmexit
> loop by about 2%.
>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Tested-by: Rik van Riel <riel@redhat.com>
--
All rights reversed
^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel entry and exit
2015-10-28 1:39 [PATCH 0/3] context_tracking: streamline code, avoid IRQ save/restore Paolo Bonzini
2015-10-28 1:39 ` [PATCH 1/3] context_tracking: remove duplicate enabled check Paolo Bonzini
2015-10-28 1:39 ` [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest entry and exit Paolo Bonzini
@ 2015-10-28 1:39 ` Paolo Bonzini
2015-10-28 5:22 ` Andy Lutomirski
2015-10-28 2:05 ` [PATCH 0/3] context_tracking: streamline code, avoid IRQ save/restore Paolo Bonzini
3 siblings, 1 reply; 14+ messages in thread
From: Paolo Bonzini @ 2015-10-28 1:39 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Andy Lutomirski, Frederic Weisbecker, Rik van Riel, Paul McKenney
x86 always calls user_enter and user_exit with interrupt disabled.
Therefore, it is not necessary to check for exceptions, nor to
save/restore the IRQ state, when context tracking functions are
called by guest_enter and guest_exit.
Use the previously introduced __context_tracking_entry and
__context_tracking_exit.
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/entry/common.c | 4 ++--
include/linux/context_tracking.h | 42 ++++++++++++++++++++++++++--------------
2 files changed, 30 insertions(+), 16 deletions(-)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 80dcc9261ca3..ba707c6da818 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -33,7 +33,7 @@
__visible void enter_from_user_mode(void)
{
CT_WARN_ON(ct_state() != CONTEXT_USER);
- user_exit();
+ __user_exit();
}
#endif
@@ -262,7 +262,7 @@ __visible void prepare_exit_to_usermode(struct pt_regs *regs)
local_irq_disable();
}
- user_enter();
+ __user_enter();
}
/*
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 68b575afe5f5..d36a5c8085b7 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -19,18 +19,6 @@ extern void context_tracking_exit(enum ctx_state state);
extern void context_tracking_user_enter(void);
extern void context_tracking_user_exit(void);
-static inline void user_enter(void)
-{
- if (context_tracking_is_enabled())
- context_tracking_enter(CONTEXT_USER);
-
-}
-static inline void user_exit(void)
-{
- if (context_tracking_is_enabled())
- context_tracking_exit(CONTEXT_USER);
-}
-
static inline enum ctx_state exception_enter(void)
{
enum ctx_state prev_ctx;
@@ -67,13 +55,39 @@ static inline enum ctx_state ct_state(void)
this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
}
#else
-static inline void user_enter(void) { }
-static inline void user_exit(void) { }
+static inline void __context_tracking_enter(enum ctx_state state) { }
+static inline void __context_tracking_exit(enum ctx_state state) { }
+static inline void context_tracking_enter(enum ctx_state state) { }
+static inline void context_tracking_exit(enum ctx_state state) { }
static inline enum ctx_state exception_enter(void) { return 0; }
static inline void exception_exit(enum ctx_state prev_ctx) { }
static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
#endif /* !CONFIG_CONTEXT_TRACKING */
+static inline void __user_enter(void)
+{
+ if (context_tracking_is_enabled())
+ __context_tracking_enter(CONTEXT_USER);
+
+}
+static inline void __user_exit(void)
+{
+ if (context_tracking_is_enabled())
+ __context_tracking_exit(CONTEXT_USER);
+}
+
+static inline void user_enter(void)
+{
+ if (context_tracking_is_enabled())
+ context_tracking_enter(CONTEXT_USER);
+
+}
+static inline void user_exit(void)
+{
+ if (context_tracking_is_enabled())
+ context_tracking_exit(CONTEXT_USER);
+}
+
#define CT_WARN_ON(cond) WARN_ON(context_tracking_is_enabled() && (cond))
#ifdef CONFIG_CONTEXT_TRACKING_FORCE
--
2.5.0
^ permalink raw reply related [flat|nested] 14+ messages in thread
* Re: [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel entry and exit
2015-10-28 1:39 ` [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel " Paolo Bonzini
@ 2015-10-28 5:22 ` Andy Lutomirski
2015-10-28 14:51 ` Paolo Bonzini
2016-03-14 19:23 ` Andy Lutomirski
0 siblings, 2 replies; 14+ messages in thread
From: Andy Lutomirski @ 2015-10-28 5:22 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm list, Andy Lutomirski, Frederic Weisbecker,
Rik van Riel, Paul McKenney
On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> x86 always calls user_enter and user_exit with interrupt disabled.
> Therefore, it is not necessary to check for exceptions, nor to
> save/restore the IRQ state, when context tracking functions are
> called by guest_enter and guest_exit.
>
> Use the previously introduced __context_tracking_entry and
> __context_tracking_exit.
x86 isn't ready for this yet. We could do a quick-and-dirty fix with
explicit IRQs-on-and-off much protected by the static key, or we could
just wait until I finish the syscall cleanup. I favor the latter, but
you're all welcome to do the former and I'll review it.
BTW, Frederic, I have a static key patch coming that I think you'll
like. I'll send it tomorrow once I'm in front of a real computer.
--Andy
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel entry and exit
2015-10-28 5:22 ` Andy Lutomirski
@ 2015-10-28 14:51 ` Paolo Bonzini
2016-03-14 19:23 ` Andy Lutomirski
1 sibling, 0 replies; 14+ messages in thread
From: Paolo Bonzini @ 2015-10-28 14:51 UTC (permalink / raw)
To: Andy Lutomirski
Cc: linux-kernel, kvm list, Andy Lutomirski, Frederic Weisbecker,
Rik van Riel, Paul McKenney
On 28/10/2015 06:22, Andy Lutomirski wrote:
>> > called by guest_enter and guest_exit.
>> >
>> > Use the previously introduced __context_tracking_entry and
>> > __context_tracking_exit.
> x86 isn't ready for this yet. We could do a quick-and-dirty fix with
> explicit IRQs-on-and-off much protected by the static key, or we could
> just wait until I finish the syscall cleanup. I favor the latter, but
> you're all welcome to do the former and I'll review it.
Or we could just do save/restore for the only call that doesn't ensure
that interrupts are disabled (syscall_trace_phase1 or whatever it's called).
But two days from the merge window, I also favor waiting until 4.5.
Paolo
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel entry and exit
2015-10-28 5:22 ` Andy Lutomirski
2015-10-28 14:51 ` Paolo Bonzini
@ 2016-03-14 19:23 ` Andy Lutomirski
2016-03-15 8:51 ` Paolo Bonzini
1 sibling, 1 reply; 14+ messages in thread
From: Andy Lutomirski @ 2016-03-14 19:23 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm list, Andy Lutomirski, Frederic Weisbecker,
Rik van Riel, Paul McKenney
On Tue, Oct 27, 2015 at 10:22 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> x86 always calls user_enter and user_exit with interrupt disabled.
>> Therefore, it is not necessary to check for exceptions, nor to
>> save/restore the IRQ state, when context tracking functions are
>> called by guest_enter and guest_exit.
>>
>> Use the previously introduced __context_tracking_entry and
>> __context_tracking_exit.
>
> x86 isn't ready for this yet. We could do a quick-and-dirty fix with
> explicit IRQs-on-and-off much protected by the static key, or we could
> just wait until I finish the syscall cleanup. I favor the latter, but
> you're all welcome to do the former and I'll review it.
>
Once Linus pulls tip:x86/asm, x86 should be ready for this. Want to try again?
--Andy
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel entry and exit
2016-03-14 19:23 ` Andy Lutomirski
@ 2016-03-15 8:51 ` Paolo Bonzini
0 siblings, 0 replies; 14+ messages in thread
From: Paolo Bonzini @ 2016-03-15 8:51 UTC (permalink / raw)
To: Andy Lutomirski
Cc: linux-kernel, kvm list, Andy Lutomirski, Frederic Weisbecker,
Rik van Riel, Paul McKenney
On 14/03/2016 20:23, Andy Lutomirski wrote:
> On Tue, Oct 27, 2015 at 10:22 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>> x86 always calls user_enter and user_exit with interrupt disabled.
>>> Therefore, it is not necessary to check for exceptions, nor to
>>> save/restore the IRQ state, when context tracking functions are
>>> called by guest_enter and guest_exit.
>>>
>>> Use the previously introduced __context_tracking_entry and
>>> __context_tracking_exit.
>>
>> x86 isn't ready for this yet. We could do a quick-and-dirty fix with
>> explicit IRQs-on-and-off much protected by the static key, or we could
>> just wait until I finish the syscall cleanup. I favor the latter, but
>> you're all welcome to do the former and I'll review it.
>>
>
> Once Linus pulls tip:x86/asm, x86 should be ready for this. Want to try again?
Yup, it's on my todo list. :)
Paolo
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH 0/3] context_tracking: streamline code, avoid IRQ save/restore
2015-10-28 1:39 [PATCH 0/3] context_tracking: streamline code, avoid IRQ save/restore Paolo Bonzini
` (2 preceding siblings ...)
2015-10-28 1:39 ` [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on kernel " Paolo Bonzini
@ 2015-10-28 2:05 ` Paolo Bonzini
3 siblings, 0 replies; 14+ messages in thread
From: Paolo Bonzini @ 2015-10-28 2:05 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Andy Lutomirski, Frederic Weisbecker, Rik van Riel, Paul McKenney
On 28/10/2015 02:39, Paolo Bonzini wrote:
> The first two of these patches were posted last February, the last one
> is new. Rik's old measurements were that it shaved around .3 microseconds
> on each iteration of his KVM benchmark.
>
> I guess three days before the start of the merge window is not
> the best time to post patches. However, I brought this series up at
> kernel summit yesterday, and Andy's cleanups actually makes it trivial
> to apply this to syscall entry. So here it is, perhaps it's worth it.
>
> Assuming it works, of course, because this is compile-tested only. :)
Heh, Andy said it doesn't. :)
However, we could still merge the first two patches for 4.4 since they
have been tested. I can even take them myself if I get Acked-by. The
third one will have to wait for 4.5.
Thanks,
Paolo
^ permalink raw reply [flat|nested] 14+ messages in thread