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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