linux-kernel - Re: [RFC PATCH 1/2] perf: Add the flag sample

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Date:	Tue, 13 Oct 2015 15:00:34 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Kaixu Xia <xiakaixu@...wei.com>, ast@...mgrid.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: [RFC PATCH 1/2] perf: Add the flag sample_disable not to output
 data on samples

Hello.

On 10/12/2015 12:02 PM, Kaixu Xia wrote:

> In some scenarios we don't want to output trace data when sampling
> to reduce overhead. This patch adds the flag sample_disable to
> implement this function. By setting this flag and integrating with
> ebpf, we can control the data output process and get the samples we
> are most interested in.
>
> Signed-off-by: Kaixu Xia <xiakaixu@...wei.com>

[...]
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 29ace10..4ae82c9 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
[...]
> 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))

    Inner parens not needed at all.

[...]

MBR, Sergei

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