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

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Date:	Fri, 18 Feb 2011 11:45:00 -0700
From:	David Ahern <daahern@...co.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 02/18/11 11:39, Peter Zijlstra wrote:
> 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

Yes, exactly. And that is what I am using -- well, -e cs -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.

On 01/23/11 at 03:45:67 a syslog event noted an application restart.
Checking the applications logs it went silent. Why? What does perf say?

Oh, 2 days have gone by before said event is reported to engineering,
and the server was been rebooted to 'clear' the problem - hence
resetting monotonic clock.

Multiply that by 100's of processes.

David

> 
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