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


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