linux-kernel - Re: [PATCH 4/4] Implement semaphore latency tracer

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Date:	Wed, 22 Oct 2008 17:48:51 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Török Edwin <edwintorok@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, sandmann@...mi.au.dk,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 4/4] Implement semaphore latency tracer


* Török Edwin <edwintorok@...il.com> wrote:

> On 2008-10-22 18:28, Ingo Molnar wrote:
> > hm, but the most common synchronization primitive are mutexes - and 
> > those are not covered by your patchset.
> >   
> 
> Indeed. I've seen a patch from Jason Baron to introduce tracepoints 
> for mutexes, but the conclusion was that the tracepoints should be in 
> lockstat instead.
> 
> And if lockstat is enabled Peter Zijlstra's 'contend with points' 
> patch seems to do exactly what I want to.
> 
> However I think it would be useful to have (a tracepoints based?) 
> latency tracker, which can be enabled/disabled at runtime, and which 
> doesn't add any data to the mutex/semaphore structures. My patchset 
> was a first attempt towards that, but it seems that such use of 
> tracepoints is not welcome at this time?
> 
> Please tell me if I should continue working on this, or if I my 
> patches are designed totally on the wrong way.

i think if you hook into Peter's lockstat APIs that should give us a 
pretty good tracer, with no ugliness introduced. That would be rather 
interesting. Peter, do you concur?

	Ingo
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