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: <56285410.3060505@huawei.com>
Date:	Thu, 22 Oct 2015 11:12:16 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	xiakaixu <xiakaixu@...wei.com>, <davem@...emloft.net>,
	<acme@...nel.org>, <mingo@...hat.com>,
	<masami.hiramatsu.pt@...achi.com>, <jolsa@...nel.org>,
	<daniel@...earbox.net>, <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 2015/10/22 11:09, Alexei Starovoitov wrote:
> On 10/21/15 6:56 PM, Wangnan (F) wrote:
>>> One alternative solution I can image is to attach a BPF program
>>> at sampling like kprobe, and return 0 if we don't want sampling
>>> take action. Thought?
>>
>> Do you think attaching BPF programs to sampling is an acceptable idea?
>
> If you mean to extend 'filter' concept to sampling events?
> So instead of soft_disable of non-local events, you'll attach bpf
> program to sampling events and use map lookup to decide whether
> to filter out or not such sampling event?

Yes.

> What pt_regs would be in such case?
>

Sampling is based on interruption. We can use pt_reg captured by the IRQ 
handler,
or we can simply pass NULL to those BPF program.

Thank you.

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