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

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Date:	Wed, 8 Feb 2012 16:07:18 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Stephane Eranian <eranian@...gle.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 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.

Is there any chance you could "perf archive" your data and upload it somewhere
I can fetch it from?

Thanks.
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