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From: Peter Zijlstra on 11 Mar 2010 03:40
On Wed, 2010-03-10 at 22:26 -0800, eranian(a)google.com wrote:
> This patch is an optimization in perf_event_task_sched_in() to avoid scheduling
> the events twice in a row. Without it, the perf_disable()/perf_enable() pair
> is invoked twice, thereby pinned events counts while scheduling flexible events
> and we go throuh hw_perf_enable() twice. By encapsulating, the whole sequence
> into perf_disable()/perf_enable() we ensure, hw_perf_enable() is going to be
> invoked only once because of the refcount protection.

Agreed, this makes perfect sense.

Acked-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl>

> Signed-off-by: Stephane Eranian <eranian(a)google.com>
> --
> perf_event.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -1382,6 +1382,8 @@ void perf_event_task_sched_in(struct task_struct *task)
> if (cpuctx->task_ctx == ctx)
> return;
>
> + perf_disable();
> +
> /*
> * We want to keep the following priority order:
> * cpu pinned (that don't need to move), task pinned,
> @@ -1394,6 +1396,8 @@ void perf_event_task_sched_in(struct task_struct *task)
> ctx_sched_in(ctx, cpuctx, EVENT_FLEXIBLE);
>
> cpuctx->task_ctx = ctx;
> +
> + perf_enable();
> }
>
> #define MAX_INTERRUPTS (~0ULL)

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