linux-kernel - Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling

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Message-ID: <5626C5CE.8080809@plumgrid.com>
Date:	Tue, 20 Oct 2015 15:53:02 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Kaixu Xia <xiakaixu@...wei.com>, davem@...emloft.net,
	acme@...nel.org, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	masami.hiramatsu.pt@...achi.com, jolsa@...nel.org,
	daniel@...earbox.net
Cc:	wangnan0@...wei.com, linux-kernel@...r.kernel.org,
	pi3orama@....com, hekuang@...wei.com, netdev@...r.kernel.org
Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY
 maps trace data output when perf sampling

On 10/20/15 12:22 AM, Kaixu Xia wrote:
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b11756f..5219635 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 (unlikely(!atomic_read(&event->soft_enable)))
> +		return 0;
> +
>   	if (event->overflow_handler)
>   		event->overflow_handler(event, data, regs);
>   	else

Peter,
does this part look right or it should be moved right after
if (unlikely(!is_sampling_event(event)))
                 return 0;
or even to other function?

It feels to me that it should be moved, since we probably don't
want to active throttling, period adjust and event_limit for events
that are in soft_disabled state.

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