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Date: Thu, 22 Oct 2015 11:12:16 +0800
From: "Wangnan (F)" <wangnan0@huawei.com>
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To: Alexei Starovoitov <ast@plumgrid.com>,
        Peter Zijlstra <peterz@infradead.org>
CC: xiakaixu <xiakaixu@huawei.com>, <davem@davemloft.net>, <acme@kernel.org>,
        <mingo@redhat.com>, <masami.hiramatsu.pt@hitachi.com>,
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        <hekuang@huawei.com>, <netdev@vger.kernel.org>
Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY
 maps trace data output when perf sampling
References: <1445325735-121694-1-git-send-email-xiakaixu@huawei.com> <1445325735-121694-2-git-send-email-xiakaixu@huawei.com> <5626C5CE.8080809@plumgrid.com> <20151021091254.GF2881@worktop.programming.kicks-ass.net> <56276968.6070604@huawei.com> <20151021113316.GM17308@twins.programming.kicks-ass.net> <56277BCE.6030400@huawei.com> <20151021121713.GC3604@twins.programming.kicks-ass.net> <56279634.5000606@huawei.com> <5628423B.4010504@huawei.com> <5628535F.5060505@plumgrid.com>
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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.