From: "Wangnan (F)" <wangnan0@huawei.com>
To: Alexei Starovoitov <ast@plumgrid.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: Tue, 13 Oct 2015 11:27:27 +0800 [thread overview]
Message-ID: <561C7A1F.6040702@huawei.com> (raw)
In-Reply-To: <561C0A1E.2080500@plumgrid.com>
On 2015/10/13 3:29, Alexei Starovoitov wrote:
> On 10/12/15 2:02 AM, Kaixu Xia wrote:
>> +extern const struct bpf_func_proto bpf_perf_event_sample_enable_proto;
>> +extern const struct bpf_func_proto bpf_perf_event_sample_disable_proto;
>
> externs are unnecessary. Just make them static.
> Also I prefer single helper that takes a flag, so we can extend it
> instead of adding func_id for every little operation.
>
> To avoid conflicts if you touch kernel/bpf/* or bpf.h please always
> base your patches of net-next.
>
> > + atomic_set(&map->perf_sample_disable, 0);
>
> global flag per map is no go.
> events are independent and should be treated as such.
>
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.
Thank you.
> Please squash these two patches, since they're part of one logical
> feature. Splitting them like this only makes review harder.
>
> --
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next prev parent reply other threads:[~2015-10-13 3:28 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) [this message]
2015-10-13 3:39 ` Alexei Starovoitov
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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