linux-kernel - Re: [PATCH 4/5] tracing/fastboot: Add a time field on the sched

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Message-ID: <48F91FE1.6030902@am.sony.com>
Date:	Fri, 17 Oct 2008 16:29:37 -0700
From:	Tim Bird <tim.bird@...sony.com>
To:	� <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH 4/5] tracing/fastboot: Add a time field on the sched_switch
 entry

� wrote:
> 2008/10/12 Fr�d�ric Weisbecker <fweisbec@...il.com>:
>> 2008/10/12 Steven Rostedt <rostedt@...dmis.org>:
>>> You can tap into the context switch trace_point too, and have that record
>>> a special trace entry for you instead.
> 
> Another thing I could do: when a sched switch entry occurs, I could
> send a special timestamp entry that
> fits my needs just before the commit of the sched entry, only if the
> current tracer is the boot tracer. This way I can output
> the appropriate timestamp just before output the sched entry.
> 
> What do you think?

I may have lost context here, but what's the purpose of the
extra timestamp again?  If it's just to have zero-based
timestamps on the ultimate output, can't you just put a single
special "start" timestamp in the trace log.  Then that can
be subtraced from all tracer-generated stamps in post-processing.
I'm not familiar enough with the tracer to know if the
post-processing is done in kernel space.  But in any event
you could use something like scripts/show_delta to get
relative timestamps (in user space).  Right now, scripts/show_delta
doesn't act like a filter - I'll have to look at that.

Sorry if I'm just adding noise...
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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