linux-kernel - Re: [PATCH 1/2 v2] tracing/function-graph-tracer: various fixes and features

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Date:	Fri, 23 Jan 2009 11:19:49 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2 v2] tracing/function-graph-tracer: various fixes
	and features


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> 
> This patch brings various bugfixes:
> 
> _ Drop the first irrelevant task switch on the very beginning of a trace.
> _ Drop the OVERHEAD word from the headers, the DURATION word is sufficient and will not
>   overlap other columns.
> _ Make the headers fit well their respective columns whatever the selected options.

> About features, one can now disable the duration (this will hide the 
> overhead too for convenient reasons and because on doesn't need overhead 
> if it hasn't the duration

very nice! I've applied this to tip/tracing/function-graph-tracer, thanks 
Frederic!

this:

> I guess no one needs the nanosec precision here, the main goal is to 
> find when happened the events on a cpu when the trace switches from one 
> cpu to another.
> 
> ie:
> 
>   274.874760 |   1)   0.676 us    |      _spin_unlock();
>   274.874762 |   1)   0.609 us    |      native_load_sp0();
>   274.874763 |   1)   0.602 us    |      native_load_tls();
>   274.878739 |   0)   0.722 us    |                  }
>   274.878740 |   0)   0.714 us    |                  native_pmd_val();
>   274.878741 |   0)   0.730 us    |                  native_pmd_val();
> 
> Here there is a 4000 usecs difference when we switch the cpu.

Still needs a solution - if we do cross-CPU traces we want to have a 
global trace clock with 'seemless' transition between CPUs.

	Ingo
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