From: Peter Zijlstra <peterz@infradead.org>
To: xiakaixu <xiakaixu@huawei.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>,
davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org,
daniel@iogearbox.net, wangnan0@huawei.com,
linux-kernel@vger.kernel.org, pi3orama@163.com,
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
Date: Wed, 21 Oct 2015 13:33:17 +0200 [thread overview]
Message-ID: <20151021113316.GM17308@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <56276968.6070604@huawei.com>
On Wed, Oct 21, 2015 at 06:31:04PM +0800, xiakaixu wrote:
> The RFC patch set contains the necessary commit log [1].
That's of course the wrong place, this should be in the patch's
Changelog. It doesn't become less relevant.
> In some scenarios we don't want to output trace data when perf sampling
> in order to reduce overhead. For example, perf can be run as daemon to
> dump trace data when necessary, such as the system performance goes down.
> Just like the example given in the cover letter, we only receive the
> samples within sys_write() syscall.
>
> The helper bpf_perf_event_control() in this patch set can control the
> data output process and get the samples we are most interested in.
> The cpu_function_call is probably too much to do from bpf program, so
> I choose current design that like 'soft_disable'.
So, IIRC, we already require eBPF perf events to be CPU-local, which
obviates the entire need for IPIs.
So calling pmu->stop() seems entirely possible (its even NMI safe).
This, however, does not explain if you need nesting, your patch seemed
to have a counter, which suggest you do.
In any case, you could add perf_event_{stop,start}_local() to mirror the
existing perf_event_read_local(), no? That would stop the entire thing
and reduce even more overhead than simply skipping the overflow handler.
> [1] https://lkml.org/lkml/2015/10/12/135
Blergh, vger should auto drop emails with lkml.org links in, that site
is getting ridiculously unreliable. (It did show the email after a
second try -- this time)
Proper links are of the form:
http://lkml.kernel.org/r/$MSGID
Those have the bonus of actually including the msgid which helps with
finding the email in local archives/mailers.
next prev parent reply other threads:[~2015-10-21 11:33 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-20 7:22 [PATCH V5 0/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Kaixu Xia
2015-10-20 7:22 ` [PATCH V5 1/1] " Kaixu Xia
2015-10-20 22:53 ` Alexei Starovoitov
2015-10-21 9:12 ` Peter Zijlstra
2015-10-21 10:31 ` xiakaixu
2015-10-21 11:33 ` Peter Zijlstra [this message]
2015-10-21 11:49 ` Wangnan (F)
2015-10-21 12:17 ` Peter Zijlstra
2015-10-21 13:42 ` Wangnan (F)
2015-10-21 13:49 ` Peter Zijlstra
2015-10-21 14:01 ` pi3orama
2015-10-21 14:09 ` Peter Zijlstra
2015-10-21 15:06 ` pi3orama
2015-10-21 16:57 ` Peter Zijlstra
2015-10-21 21:19 ` Alexei Starovoitov
2015-10-22 9:06 ` Peter Zijlstra
2015-10-22 10:28 ` Wangnan (F)
2015-10-23 12:52 ` Peter Zijlstra
2015-10-23 15:12 ` Peter Zijlstra
2015-10-27 6:43 ` xiakaixu
2015-10-22 2:46 ` Wangnan (F)
2015-10-22 7:39 ` Ingo Molnar
2015-10-22 7:51 ` Wangnan (F)
2015-10-22 9:24 ` Peter Zijlstra
2015-10-22 1:56 ` Wangnan (F)
2015-10-22 3:09 ` Alexei Starovoitov
2015-10-22 3:12 ` Wangnan (F)
2015-10-22 3:26 ` Alexei Starovoitov
2015-10-22 9:49 ` Peter Zijlstra
2015-10-21 11:34 ` Wangnan (F)
2015-10-21 11:56 ` Peter Zijlstra
2015-10-21 12:03 ` Wangnan (F)
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