Re: [RFC PATCH 1/2] perf: Add the flag sample_disable not to output data on samples

[Wangnan (F)]

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?

Thank you.

I think we should at the very least replace the kzalloc() currently used
with a cacheline aligned alloc, and check the structure layout to verify
these two do in fact share a cacheline.

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