linux-kernel - Re: [tip:perf/urgent] perf_events: Fix time tracking for events with pid != -1 and cpu != -1

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Date:	Tue, 31 Aug 2010 10:03:33 +0200
From:	stephane eranian <eranian@...glemail.com>
To:	Lin Ming <lin@...g.vg>
Cc:	mingo@...hat.com, hpa@...or.com, eranian@...gle.com,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	tglx@...utronix.de, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf_events: Fix time tracking for events with
 pid != -1 and cpu != -1

On Tue, Aug 31, 2010 at 3:10 AM, Lin Ming <lin@...g.vg> wrote:
>>
>> perf_events: Fix time tracking for events with pid != -1 and cpu != -1
>
> Hi,
>
> I thought pid != -1 and cpu != -1 is not valid.
>

This is in per-thread mode. This is what happens when you do
perf record foo for instance. This is sampling, but you can do
the same with counting.


> # perf top -p 23268 -C 1
> WARNING: PID switch overriding CPU
>
> In which case this could be valid?
>
> Thanks,
> Lin Ming
>
>>
>> Per-thread events with a cpu filter, i.e., cpu != -1, were not
>> reporting correct timings when the thread never ran on the
>> monitored cpu. The time enabled was reported as a negative
>> value.
>
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