Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable() helpers

From	Alexei Starovoitov <ast@plumgrid.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable() helpers
Date	2015-10-13 05:40 +0200
Message-ID	<qiYBr-2Ii-5@gated-at.bofh.it> (permalink)
References	<qiHhh-2LN-29@gated-at.bofh.it> <qiHhh-2LN-27@gated-at.bofh.it> <qiQXg-8t1-13@gated-at.bofh.it> <qiYrL-2vS-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 10/12/15 8:27 PM, Wangnan (F) wrote:
> Then how to avoid racing? For example, when one core disabling all events
> in a map, another core is enabling all of them. This racing may causes
> sereval
> perf events in a map dump samples while other events not. To avoid such
> racing
> I think some locking must be introduced, then cost is even higher.
>
> The reason why we introduce an atomic pointer is because each operation
> should
> controls a set of events, not one event, due to the per-cpu manner of
> perf events.

why 'set disable' is needed ?
the example given in cover letter shows the use case where you want
to receive samples only within sys_write() syscall.
The example makes sense, but sys_write() is running on this cpu, so just
disabling it on the current one is enough.

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Thread

[RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable() helpers Kaixu Xia <xiakaixu@huawei.com> - 2015-10-12 11:10 +0200
  Re: [RFC PATCH 2/2] bpf: Implement  bpf_perf_event_sample_enable/disable() helpers Alexei Starovoitov <ast@plumgrid.com> - 2015-10-12 21:30 +0200
    Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable()  helpers "Wangnan (F)" <wangnan0@huawei.com> - 2015-10-13 05:30 +0200
      Re: [RFC PATCH 2/2] bpf: Implement  bpf_perf_event_sample_enable/disable() helpers Alexei Starovoitov <ast@plumgrid.com> - 2015-10-13 05:40 +0200
        Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable()  helpers "Wangnan (F)" <wangnan0@huawei.com> - 2015-10-13 06:00 +0200
          Re: [RFC PATCH 2/2] bpf: Implement  bpf_perf_event_sample_enable/disable() helpers Alexei Starovoitov <ast@plumgrid.com> - 2015-10-13 06:20 +0200
            Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable()  helpers "Wangnan (F)" <wangnan0@huawei.com> - 2015-10-13 06:40 +0200
              Re: [RFC PATCH 2/2] bpf: Implement  bpf_perf_event_sample_enable/disable() helpers Alexei Starovoitov <ast@plumgrid.com> - 2015-10-13 07:20 +0200
                Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable()  helpers "Wangnan (F)" <wangnan0@huawei.com> - 2015-10-13 09:10 +0200
                Re: [RFC PATCH 2/2] bpf: Implement  bpf_perf_event_sample_enable/disable() helpers He Kuang <hekuang@huawei.com> - 2015-10-13 13:00 +0200
                Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable()  helpers "Wangnan (F)" <wangnan0@huawei.com> - 2015-10-13 13:20 +0200
                Re: [RFC PATCH 2/2] bpf: Implement  bpf_perf_event_sample_enable/disable() helpers Alexei Starovoitov <ast@plumgrid.com> - 2015-10-14 07:20 +0200

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