linux-kernel - Re: [PATCH 2/2] tracing/branch-tracer: adapt to the stat tracing API

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Date:	Wed, 7 Jan 2009 23:49:49 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 2/2] tracing/branch-tracer: adapt to the stat tracing
 API

On Sat, 27 Dec 2008, Frederic Weisbecker wrote:

> This patch adapts the branch tracer to the tracing API.
> This is not really for inclusion but more likely a proof of concept because
> the branch tracer implements two "stat tracing" that were split in two files.
> 
> So I added an option to the branch tracer: stat_all_branch.
> If it is set, then trace_stat will output all of the branches entries stats.
> Otherwise, it will print the annotated branches.
> 
> Its is a kind of quick trick, waiting for a better solution.
> By default, the annotated branches stat are sorted by incorrect branch prediction
> percentage.
> 

OK, I have not had a chance to look at this code since it was sent when I 
was on Holiday. But I do not think that the only way to see the output of 
a histogram is to set it in the current_tracer. If I have the branch 
tracer on, I would have to run it to see the output of the histogram.

The histogram starts recording at boot up. Although the branch tracer is 
dependent on the histograms, the histogram is not dependent on the branch 
tracer. This code is making the histogram dependent on the trace. It took 
me a while to figure out how to see my histogram.

With the new patches (after the compile issue is solved) we could have a 
register_histogram or something that would put the file in the trace_stats 
directory. This would separate the need of coupling the tracers with the 
histogram even when they are not coupled.

-- Steve

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