On Mon, Oct 12, 2015 at 08:05:20PM +0800, Wangnan (F) wrote:
>
>
> On 2015/10/12 20:02, Peter Zijlstra wrote:
> >On Mon, Oct 12, 2015 at 09:02:42AM +0000, Kaixu Xia wrote:
> >>--- a/include/linux/perf_event.h
> >>+++ b/include/linux/perf_event.h
> >>@@ -483,6 +483,8 @@ struct perf_event {
> >> perf_overflow_handler_t overflow_handler;
> >> void *overflow_handler_context;
> >>+ atomic_t *sample_disable;
> >>+
> >> #ifdef CONFIG_EVENT_TRACING
> >> struct trace_event_call *tp_event;
> >> struct event_filter *filter;
> >>diff --git a/kernel/events/core.c b/kernel/events/core.c
> >>index b11756f..f6ef45c 100644
> >>--- a/kernel/events/core.c
> >>+++ b/kernel/events/core.c
> >>@@ -6337,6 +6337,9 @@ static int __perf_event_overflow(struct perf_event
> >>*event,
> >> irq_work_queue(&event->pending);
> >> }
> >>+ if ((event->sample_disable) && atomic_read(event->sample_disable))
> >>+ return ret;
> >>+
> >> if (event->overflow_handler)
> >> event->overflow_handler(event, data, regs);
> >> else
> >Try and guarantee sample_disable lives in the same cacheline as
> >overflow_handler.
>
> Could you please explain why we need them to be in a same cacheline?
Because otherwise you've just added a cacheline miss to this relatively
hot path.
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