linux-kernel - Re: [BUG] perf: perf sched warning possibly due to clock granularity on AMD

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Date:	Wed, 8 Feb 2012 16:10:24 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com,
	peterz@...radead.org, mingo@...e.hu, robert.richter@....com,
	eric.dumazet@...il.com
Subject: Re: [BUG] perf: perf sched warning possibly due to clock granularity
 on AMD

On Wed, Feb 8, 2012 at 4:07 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Mon, Feb 06, 2012 at 02:25:46PM +0100, Stephane Eranian wrote:
>> Hi,
>>
>> I am running 3.3.30-rc2 on an AMD Bulldozer system in 64-bit mode.
>> I was testing perf sched and I ran into an issue. That issue seems
>> to exist only on AMD and not on Intel systems. It is not PMU related
>> because I am doing tracing.
>>
>> I am running a simple ping pong test to stress the context switch
>> code. Two processes exchanging a byte through a pipe (program provided
>> below).
>>
>> Then, I capture a trace using perf sched, and I run sched lat, but
>> on certain runs, I get:
>>
>>    $ perf sched rec pong 2
>>    $ perf sched lat
>>      Warning: Timestamp below last timeslice flush
>>      Warning: Timestamp below last timeslice flush
>>      Warning: Timestamp below last timeslice flush
>>      Warning: Timestamp below last timeslice flush
>>      Warning: Timestamp below last timeslice flush
>>      Warning: Timestamp below last timeslice flush
>>      Warning: Timestamp below last timeslice flush
>>      Warning: Timestamp below last timeslice flush
>>      Warning: TimesFound 4934 unknown events!
>>      Is this an older tool processing a perf.data file generated by a more recent tool?
>
> I've tried to reproduce this on an AMD phenom but haven't got any such
> warning.
>
It does not happen at each run.

> Is there any chance you could "perf archive" your data and upload it somewhere
> I can fetch it from?
>
I can send you the perf.data in a private Email.
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