linux-kernel - Re: [PATCH 3/3] perf events: add timehist option to record and report

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Message-ID: <1298054399.5226.779.camel@laptop>
Date:	Fri, 18 Feb 2011 19:39:59 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <daahern@...co.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, acme@...stprotocols.net,
	paulus@...ba.org, Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 3/3] perf events: add timehist option to record and
 report

On Fri, 2011-02-18 at 11:07 -0700, David Ahern wrote:
> We want not only context-switch events, but the stack trace at the
> switch. 

Both ftrace and perf can do that:

 perf record -ge sched:sched_switch -c 1

or

echo 1 > /debug/tracing/options/stacktrace

> That data along with the gettimeofday timestamp has allowed us to
> resolve performance issues such as a system call taking longer than
> expected during a specific sequence of events or a process getting
> preempted and not scheduled for N seconds. etc., etc.

Non of that seems to require GTOD stamps.

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