From: Alexei Starovoitov <ast@plumgrid.com>
To: "Wangnan (F)" <wangnan0@huawei.com>,
Kaixu Xia <xiakaixu@huawei.com>,
davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
a.p.zijlstra@chello.nl, masami.hiramatsu.pt@hitachi.com,
jolsa@kernel.org, daniel@iogearbox.net
Cc: linux-kernel@vger.kernel.org, pi3orama@163.com,
hekuang@huawei.com, netdev@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable() helpers
Date: Mon, 12 Oct 2015 20:39:06 -0700 [thread overview]
Message-ID: <561C7CDA.8050004@plumgrid.com> (raw)
In-Reply-To: <561C7A1F.6040702@huawei.com>
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.
next prev parent reply other threads:[~2015-10-13 3:39 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-12 9:02 [RFC PATCH 0/2] bpf: enable/disable events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Kaixu Xia
2015-10-12 9:02 ` [RFC PATCH 1/2] perf: Add the flag sample_disable not to output data on samples Kaixu Xia
2015-10-12 12:02 ` Peter Zijlstra
2015-10-12 12:05 ` Wangnan (F)
2015-10-12 12:12 ` Peter Zijlstra
2015-10-12 14:14 ` kbuild test robot
2015-10-12 19:20 ` Alexei Starovoitov
2015-10-13 2:30 ` xiakaixu
2015-10-13 3:10 ` Alexei Starovoitov
2015-10-13 12:00 ` Sergei Shtylyov
2015-10-12 9:02 ` [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable() helpers Kaixu Xia
2015-10-12 19:29 ` Alexei Starovoitov
2015-10-13 3:27 ` Wangnan (F)
2015-10-13 3:39 ` Alexei Starovoitov [this message]
2015-10-13 3:51 ` Wangnan (F)
2015-10-13 4:16 ` Alexei Starovoitov
2015-10-13 4:34 ` Wangnan (F)
2015-10-13 5:15 ` Alexei Starovoitov
2015-10-13 6:57 ` Wangnan (F)
2015-10-13 10:54 ` He Kuang
2015-10-13 11:07 ` Wangnan (F)
2015-10-14 5:14 ` Alexei Starovoitov
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