From: Peter Zijlstra <peterz@infradead.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@elte.hu>, Borislav Petkov <bp@amd64.org>,
Venki Pallipadi <venki@google.com>,
Stephane Eranian <eranian@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@infradead.org>,
Robert Richter <robert.richter@amd.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
Andreas Herrmann <andreas.herrmann3@amd.com>
Subject: Re: [PATCH] x86, AMD: Set sched_clock_stable
Date: Wed, 15 Feb 2012 16:30:37 +0100 [thread overview]
Message-ID: <1329319837.2293.143.camel@twins> (raw)
In-Reply-To: <1328616532-13783-1-git-send-email-bp@alien8.de>
On Tue, 2012-02-07 at 13:08 +0100, Borislav Petkov wrote:
> Stephane Eranian reported that doing a scheduler latency measurements
> with perf on AMD doesn't work out as expected due to the fact that the
> sched_clock() granularity is too coarse, i.e. done in jiffies due to the
> sched_clock_stable not set, which, if set, would mean that we get to use
> the TSC as sample source which would give us much higher precision.
FWIW that's not entirely accurate, the problem with !sched_clock_stable
is that the time between CPUs can drift a little. So while timestamps on
the same CPU are high-res, when comparing them across CPUs you can
observe funnies.
next prev parent reply other threads:[~2012-02-15 15:31 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-06 13:25 [BUG] perf: perf sched warning possibly due to clock granularity on AMD Stephane Eranian
2012-02-06 14:26 ` Peter Zijlstra
2012-02-06 14:31 ` Stephane Eranian
2012-02-06 17:17 ` Arnaldo Carvalho de Melo
2012-02-06 15:34 ` Borislav Petkov
2012-02-06 16:37 ` Peter Zijlstra
2012-02-06 16:46 ` Borislav Petkov
2012-02-06 16:54 ` Peter Zijlstra
2012-02-06 20:27 ` Borislav Petkov
2012-02-06 20:31 ` Peter Zijlstra
2012-02-06 20:37 ` Borislav Petkov
2012-02-06 21:19 ` Venki Pallipadi
2012-02-07 7:51 ` Peter Zijlstra
2012-02-07 8:32 ` Ingo Molnar
2012-02-07 9:06 ` Borislav Petkov
2012-02-07 9:50 ` Ingo Molnar
2012-02-07 12:08 ` [PATCH] x86, AMD: Set sched_clock_stable Borislav Petkov
2012-02-15 15:30 ` Peter Zijlstra [this message]
2012-02-07 19:43 ` [tip:perf/core] x86/sched/perf/AMD: " tip-bot for Borislav Petkov
2012-02-08 15:07 ` [BUG] perf: perf sched warning possibly due to clock granularity on AMD Frederic Weisbecker
2012-02-08 15:10 ` Stephane Eranian
2012-02-08 15:22 ` Frederic Weisbecker
2012-02-08 15:23 ` Stephane Eranian
2012-02-18 16:50 ` [PATCH] perf tools: Fix ordering with unstable tsc Frederic Weisbecker
2012-02-22 15:35 ` Stephane Eranian
2012-02-22 15:39 ` David Ahern
2012-03-05 18:43 ` Frederic Weisbecker
2012-03-14 19:55 ` Arnaldo Carvalho de Melo
2012-03-14 20:07 ` David Ahern
2012-03-22 0:10 ` Frederic Weisbecker
2012-03-22 15:28 ` Arnaldo Carvalho de Melo
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