[PATCH 1/2] perf: fix PERF_EVENT_IOC_PERIOD to force-reset the period

[PATCH 1/2] perf: fix PERF_EVENT_IOC_PERIOD to force-reset the period

[Will Deacon]

From: Peter Zijlstra <peterz@infradead.org>

Vince Weaver reports that, on all architectures apart from ARM,
PERF_EVENT_IOC_PERIOD doesn't actually update the period until the next
event fires. This is counter-intuitive behaviour and is better dealt
with in the core code.

This patch ensures that the period is forcefully reset when dealing with
such a request in the core code. A subsequent patch removes the
equivalent hack from the ARM back-end.

Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---

Peter -- I didn't want this to get lost, so I picked it up, fixed a typo
         and wrote a commit message. Could I add your SoB please?

	 Cheers,
		Will

 kernel/events/core.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d724e7757cd1..1c626b923ddf 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3527,7 +3527,7 @@ static void perf_event_for_each(struct perf_event *event,
 static int perf_event_period(struct perf_event *event, u64 __user *arg)
 {
 	struct perf_event_context *ctx = event->ctx;
-	int ret = 0;
+	int ret = 0, active;
 	u64 value;
 
 	if (!is_sampling_event(event))
@@ -3551,6 +3551,20 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
 		event->attr.sample_period = value;
 		event->hw.sample_period = value;
 	}
+
+	active = (event->state == PERF_EVENT_STATE_ACTIVE);
+	if (active) {
+		perf_pmu_disable(ctx->pmu);
+		event->pmu->stop(event, PERF_EF_UPDATE);
+	}
+
+	local64_set(&event->hw.period_left, 0);
+
+	if (active) {
+		event->pmu->start(event, PERF_EF_RELOAD);
+		perf_pmu_enable(ctx->pmu);
+	}
+
 unlock:
 	raw_spin_unlock_irq(&ctx->lock);
 
-- 
1.8.2.2

[PATCH 2/2] Revert "ARM: 7556/1: perf: fix updated event period in response to PERF_EVENT_IOC_PERIOD"

[Will Deacon]

This reverts commit 3581fe0ef37ce12ac7a4f74831168352ae848edc.

Updates to the handling of PERF_EVENT_IOC_PERIOD in the core code mean
we no longer have to play this horrible game.

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/kernel/perf_event.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index bc3f2efa0d86..789d846a9184 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -99,10 +99,6 @@ int armpmu_event_set_period(struct perf_event *event)
 	s64 period = hwc->sample_period;
 	int ret = 0;
 
-	/* The period may have been changed by PERF_EVENT_IOC_PERIOD */
-	if (unlikely(period != hwc->last_period))
-		left = period - (hwc->last_period - left);
-
 	if (unlikely(left <= -period)) {
 		left = period;
 		local64_set(&hwc->period_left, left);
-- 
1.8.2.2

[tip:perf/core] Revert "ARM: 7556/1: perf: fix updated event period in response to PERF_EVENT_IOC_PERIOD"

[tip-bot for Will Deacon]

Commit-ID:  9450d14fb959336803e5209119eb422b667b96aa
Gitweb:     http://git.kernel.org/tip/9450d14fb959336803e5209119eb422b667b96aa
Author:     Will Deacon <will.deacon@arm.com>
AuthorDate: Wed, 27 Nov 2013 13:54:39 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 17 Dec 2013 15:21:35 +0100

Revert "ARM: 7556/1: perf: fix updated event period in response to PERF_EVENT_IOC_PERIOD"

This reverts commit 3581fe0ef37ce12ac7a4f74831168352ae848edc.

Fixes to the handling of PERF_EVENT_IOC_PERIOD in the core code mean
we no longer have to play this horrible game.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1385560479-11014-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/arm/kernel/perf_event.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index bc3f2ef..789d846 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -99,10 +99,6 @@ int armpmu_event_set_period(struct perf_event *event)
 	s64 period = hwc->sample_period;
 	int ret = 0;
 
-	/* The period may have been changed by PERF_EVENT_IOC_PERIOD */
-	if (unlikely(period != hwc->last_period))
-		left = period - (hwc->last_period - left);
-
 	if (unlikely(left <= -period)) {
 		left = period;
 		local64_set(&hwc->period_left, left);

Re: [PATCH 1/2] perf: fix PERF_EVENT_IOC_PERIOD to force-reset the period

[Vince Weaver]

On Wed, 27 Nov 2013, Will Deacon wrote:

> Vince Weaver reports that, on all architectures apart from ARM,
> PERF_EVENT_IOC_PERIOD doesn't actually update the period until the next
> event fires. This is counter-intuitive behaviour and is better dealt
> with in the core code.

To be fair, it was Andreas Sandberg <andreas.sandberg@it.uu.se>
who noticed this issue and reported it to me (in the context of 
the manpage being wrong).  I just passed it on to the linux-kernel list.

Vince

Re: [PATCH 1/2] perf: fix PERF_EVENT_IOC_PERIOD to force-reset the period

[Will Deacon]

Hi Peter,

Do you have any thoughts on the below? It would be good to add your
signed-off to the patch, since you wrote it originally.

Cheers,

Will

On Wed, Nov 27, 2013 at 01:54:38PM +0000, Will Deacon wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> 
> Vince Weaver reports that, on all architectures apart from ARM,
> PERF_EVENT_IOC_PERIOD doesn't actually update the period until the next
> event fires. This is counter-intuitive behaviour and is better dealt
> with in the core code.
> 
> This patch ensures that the period is forcefully reset when dealing with
> such a request in the core code. A subsequent patch removes the
> equivalent hack from the ARM back-end.
> 
> Cc: Vince Weaver <vincent.weaver@maine.edu>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> ---
> 
> Peter -- I didn't want this to get lost, so I picked it up, fixed a typo
>          and wrote a commit message. Could I add your SoB please?
> 
> 	 Cheers,
> 		Will
> 
>  kernel/events/core.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index d724e7757cd1..1c626b923ddf 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3527,7 +3527,7 @@ static void perf_event_for_each(struct perf_event *event,
>  static int perf_event_period(struct perf_event *event, u64 __user *arg)
>  {
>  	struct perf_event_context *ctx = event->ctx;
> -	int ret = 0;
> +	int ret = 0, active;
>  	u64 value;
>  
>  	if (!is_sampling_event(event))
> @@ -3551,6 +3551,20 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
>  		event->attr.sample_period = value;
>  		event->hw.sample_period = value;
>  	}
> +
> +	active = (event->state == PERF_EVENT_STATE_ACTIVE);
> +	if (active) {
> +		perf_pmu_disable(ctx->pmu);
> +		event->pmu->stop(event, PERF_EF_UPDATE);
> +	}
> +
> +	local64_set(&event->hw.period_left, 0);
> +
> +	if (active) {
> +		event->pmu->start(event, PERF_EF_RELOAD);
> +		perf_pmu_enable(ctx->pmu);
> +	}
> +
>  unlock:
>  	raw_spin_unlock_irq(&ctx->lock);
>  
> -- 
> 1.8.2.2
> 

Re: [PATCH 1/2] perf: fix PERF_EVENT_IOC_PERIOD to force-reset the period

[Peter Zijlstra]

On Thu, Dec 12, 2013 at 06:27:47PM +0000, Will Deacon wrote:
> Hi Peter,
> 
> Do you have any thoughts on the below? It would be good to add your
> signed-off to the patch, since you wrote it originally.
> 

Picked them up, thanks will!

[tip:perf/core] perf: Fix PERF_EVENT_IOC_PERIOD to force-reset the period

[tip-bot for Peter Zijlstra]

Commit-ID:  bad7192b842c83e580747ca57104dd51fe08c223
Gitweb:     http://git.kernel.org/tip/bad7192b842c83e580747ca57104dd51fe08c223
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 27 Nov 2013 13:54:38 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 17 Dec 2013 15:21:33 +0100

perf: Fix PERF_EVENT_IOC_PERIOD to force-reset the period

Vince Weaver reports that, on all architectures apart from ARM,
PERF_EVENT_IOC_PERIOD doesn't actually update the period until the next
event fires. This is counter-intuitive behaviour and is better dealt
with in the core code.

This patch ensures that the period is forcefully reset when dealing with
such a request in the core code. A subsequent patch removes the
equivalent hack from the ARM back-end.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/1385560479-11014-1-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/core.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 403b781..89d34f9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3527,7 +3527,7 @@ static void perf_event_for_each(struct perf_event *event,
 static int perf_event_period(struct perf_event *event, u64 __user *arg)
 {
 	struct perf_event_context *ctx = event->ctx;
-	int ret = 0;
+	int ret = 0, active;
 	u64 value;
 
 	if (!is_sampling_event(event))
@@ -3551,6 +3551,20 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
 		event->attr.sample_period = value;
 		event->hw.sample_period = value;
 	}
+
+	active = (event->state == PERF_EVENT_STATE_ACTIVE);
+	if (active) {
+		perf_pmu_disable(ctx->pmu);
+		event->pmu->stop(event, PERF_EF_UPDATE);
+	}
+
+	local64_set(&event->hw.period_left, 0);
+
+	if (active) {
+		event->pmu->start(event, PERF_EF_RELOAD);
+		perf_pmu_enable(ctx->pmu);
+	}
+
 unlock:
 	raw_spin_unlock_irq(&ctx->lock);