Subject: Re: [PATCH 3/3] perf events: add timehist option to record and
 report
From: Peter Zijlstra <peterz@infradead.org>
To: David Ahern <daahern@cisco.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        acme@ghostprotocols.net, paulus@samba.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Arnaldo Carvalho de Melo <acme@redhat.com>
In-Reply-To: <4D5EB564.6030504@cisco.com>
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Date: Fri, 18 Feb 2011 19:39:59 +0100
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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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