linux-kernel - Re: [PATCH] new irq tracer

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Date:	Wed, 18 Feb 2009 22:15:25 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	mingo@...e.hu, rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	acme@...stprotocols.net, fweisbec@...il.com, fche@...hat.com,
	compudj@...stal.dyndns.org
Subject: Re: [PATCH] new irq tracer

On Wed, 2009-02-18 at 14:53 -0500, Jason Baron wrote:
> hi,
> 
> Using a copule of tracepoints i've implemented an 'irq tracer' which has
> the following column format:
> 
> [time][irq][action][handled][cpu][length]
> 
> for example on my system:
> 
> [ 1038.927248381]     28     eth0      1        3     0.000002745
> [ 1038.927544688]     28     eth0      1        3     0.000002520
> [ 1038.927593609]     28     eth0      1        3     0.000002509
> [ 1038.974087675]     29     ahci      1        1     0.000013135
> [ 1038.974288475]     29     ahci      1        1     0.000005542
> [ 1038.974414324]     29     ahci      1        1     0.000007953
> 
> I think this patch is useful in understanding irq system behavior, and
> for tracking down irq driver handlers that are firing too often or
> spending too much time handling an irq. This approach could be extended
> to the timer irq and for softirqs...

The function graph tracer can already do this, it has a special section
to recognize irq entry function, and already measures time spend.

I guess with Steve's new triggers (probes or whatever they ended up
being called) you could limit it to just IRQ entry points.



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