From: Alexander Yarygin <yarygin@linux.vnet.ibm.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>,
linux-kernel@vger.kernel.org,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
David Ahern <dsahern@gmail.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Mike Galbraith <efault@gmx.de>,
Namhyung Kim <namhyung.kim@lge.com>,
Paul Mackerras <paulus@samba.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Stephane Eranian <eranian@google.com>,
Alexander Yarygin <yarygin@linux.vnet.ibm.com>
Subject: Re: [PATCH 1/2] perf tools: Add option to copy events when queueing
Date: Fri, 03 Oct 2014 18:25:15 +0400 [thread overview]
Message-ID: <87iok1cjsk.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <20141003084754.GA29966@gmail.com> (Ingo Molnar's message of "Fri, 3 Oct 2014 10:47:54 +0200")
Ingo Molnar <mingo@kernel.org> writes:
> * Jiri Olsa <jolsa@redhat.com> wrote:
>
>> On Fri, Oct 03, 2014 at 06:34:21AM +0200, Ingo Molnar wrote:
>> >
>> > * Alexander Yarygin <yarygin@linux.vnet.ibm.com> wrote:
>> >
[..]
>> >
>> > What's the performance effect of this - i.e. by how much does CPU
>> > use increase due to copying the events?
>> >
>> > Wouldn't it be faster to fix this problem by updating the mmap
>> > tail pointer only once the event has truly been consumed?
>>
>> Alexander mentioned he'd loose data, because of userspace
>> processing being to slow:
>>
>> http://marc.info/?l=linux-kernel&m=141111652424818&w=2
>
> So copying helps by allocating an essentially larger buffer, to
> hold all unprocessed events that user-space is too slow to
> process?
>
> I guess it's a valid usecase.
>
> Thanks,
>
> Ingo
Right. Also, it looks like the overhead here isn't a big deal:
time needed for actual processing an event is significantly bigger
and the additional memdup() doesn't change that much.
next prev parent reply other threads:[~2014-10-03 14:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-02 16:38 [PATCH v3 0/2] perf kvm stat live: Copy events Alexander Yarygin
2014-10-02 16:38 ` [PATCH 1/2] perf tools: Add option to copy events when queueing Alexander Yarygin
2014-10-03 4:34 ` Ingo Molnar
2014-10-03 6:50 ` Jiri Olsa
2014-10-03 8:47 ` Ingo Molnar
2014-10-03 14:25 ` Alexander Yarygin [this message]
2014-10-03 7:33 ` Jiri Olsa
2014-10-02 16:38 ` [PATCH 2/2] perf kvm stat live: Enable events copying Alexander Yarygin
-- strict thread matches above, loose matches on Subject: below --
2014-10-03 14:40 [PATCH v4 0/2] perf kvm stat live: Copy events Alexander Yarygin
2014-10-03 14:40 ` [PATCH 1/2] perf tools: Add option to copy events when queueing Alexander Yarygin
2014-10-02 10:32 [PATCH v2 0/2] perf kvm stat live: Copy events Alexander Yarygin
2014-10-02 10:32 ` [PATCH 1/2] perf tools: Add option to copy events when queueing Alexander Yarygin
2014-10-02 14:15 ` Jiri Olsa
2014-10-02 15:21 ` Alexander Yarygin
2014-10-02 15:33 ` Jiri Olsa
2014-10-02 15:45 ` David Ahern
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