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

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Date:	Wed, 22 Oct 2008 20:25:30 +0300
From:	Török Edwin <edwintorok@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>, 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

On 2008-10-22 20:22, Peter Zijlstra wrote:
> On Wed, 2008-10-22 at 17:48 +0200, Ingo Molnar wrote:
>   
>> * 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?
>>     
>
> Yes, I've already suggested this. Use the exact same hooks that
> lockdep/lockstat use.

Ok, I'll work on this when I get some time :)
[hopefully this weekend test the 'contend with points patch', next
weekend write the new tracepoints]

Best regards,
--Edwin
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