linux-kernel - Re: [PATCH 3/6] perf: Add timestamp to COMM and MMAP events

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Message-ID: <20101130140213.GB9217@ghostprotocols.net>
Date:	Tue, 30 Nov 2010 12:02:13 -0200
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Ian Munsie <imunsie@....ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 3/6] perf: Add timestamp to COMM and MMAP events

Em Tue, Nov 30, 2010 at 10:45:40AM +1100, Ian Munsie escreveu:
> Excerpts from Peter Zijlstra's message of Mon Nov 29 22:54:50 +1100 2010:
> > On Mon, 2010-11-29 at 17:06 +1100, Ian Munsie wrote:
> > > This goes away if PERF_SAMPLE_CPU is added to the mix so that the
> > > timestamps are offset from the first event of *their* CPU,
> > > otherwise time-epoch can go negative, as it has done here. 

> > How does that happen, I though the power7 sched_clock() was fully
> > synchronized and monotonic across all cores?

> Oh the timestamps coming from the kernel are fine, I should have been
> clearer in my email. This bug is purely restricted to the userspace code
> that prints them out - in the perf_session__print_tstamp function. It
> tries to print the timestamps out so that they start at 0 and if it
> doesn't know what CPU the events came from it uses the very first event
> it sees as epoch, but at the moment that is not necessarily going to be
> the earliest event.
 
> Thinking about it overnight, I realise that this should also go away if
> we sort them before printing things out at all, which is exactly what
> I'm proposing to do in my patches.

I removed that in the current version of this patch series:

http://git.kernel.org/?p=linux/kernel/git/acme/linux-2.6.git;a=shortlog;h=refs/heads/perf/sample_id_all.v3

Now I'm just testing if a new perf.data file can be processed just fine
by older tools (not possible in the sample_id_all.v1 series) and other
combinations of older kernels with the new tool.

Probably I'll fold two patches and then submit for review.

- Arnaldo
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