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

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Message-ID: <20120208152200.GC25473@somewhere.redhat.com>
Date:	Wed, 8 Feb 2012 16:22:03 +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 Wed, Feb 08, 2012 at 04:10:24PM +0100, Stephane Eranian wrote:
> 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.

Yeah I tried 5 times but wasn't lucky.

> 
> > 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.

Thanks!
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