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Message-ID: <20090317152753.GD13895@elte.hu>
Date: Tue, 17 Mar 2009 16:27:53 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Miklos Szeredi <miklos@...redi.hu>,
Frédéric Weisbecker <fweisbec@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: rostedt@...dmis.org, linux-kernel@...r.kernel.org
Subject: Re: wrong timestamps in ftrace?
* Miklos Szeredi <miklos@...redi.hu> wrote:
> I've started playing with ftrace and timestamps seem to be
> misbehaving.
>
> # echo 0 > /sys/kernel/debug/tracing/tracing_enabled
> # echo nop > /sys/kernel/debug/tracing/current_tracer
> # echo 131072 > /sys/kernel/debug/tracing/buffer_size_kb
> # echo sched_switch > /sys/kernel/debug/tracing/current_tracer
> # echo 1 > /sys/kernel/debug/tracing/tracing_enabled
> # sleep 10
> # echo 0 > /sys/kernel/debug/tracing/tracing_enabled
> # cat /sys/kernel/debug/tracing/trace > /tmp/trace.txt
> # ls -lh /tmp/trace.txt
> -rw-r--r-- 1 root root 96K Mar 17 16:11 /tmp/trace.txt
> # head -5 /tmp/trace.txt | tail -1
> bash-4908 [001] 212.139730: 4908:120:S + [001] 4845:120:S
> # tail -1 /tmp/trace.txt
> kondemand/1-1020 [001] 212.261054: 1020:115:S ==> [001] 0:140:R
>
> So according to the timestamps the time difference between the first
> and last event was just 0.12s, which is rubbish.
>
> This is latest git on a CoreDuo T60 notebook. Attaching .config and
> dmesg.
There's been changes to timestamping in the tracing tree. Could you
check whether latest -tip:
http://people.redhat.com/mingo/tip.git/README
works better for you?
Ingo
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