Subject: Re: [PATCH 4/4] Implement semaphore latency tracer
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: =?ISO-8859-1?Q?T=F6r=F6k?= Edwin <edwintorok@gmail.com>
Cc: mingo@elte.hu, sandmann@daimi.au.dk, linux-kernel@vger.kernel.org,
       Steven Rostedt <rostedt@goodmis.org>,
       Arjan van de Ven <arjan@infradead.org>
In-Reply-To: <1223817124-27239-6-git-send-email-edwintorok@gmail.com>
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	 <1223817124-27239-6-git-send-email-edwintorok@gmail.com>
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Date: Sun, 12 Oct 2008 21:13:06 +0200
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On Sun, 2008-10-12 at 16:12 +0300, Török Edwin wrote:
> Each time a down_read or down_write fails, a unique latency id is generated.
> Later when someone releases the semaphore, it is blamed for the latency of all
> tasks on the wait_list of the semaphore.
> If you would group the output from latency_trace by the latency_id you get all those
> who were contending on a lock, and the tasks that were holding the lock.
> An entry in latency_trace has the format:
> (latency_id) [semaphore_id] read|write
> stacktrace <= stacktrace

What can this tracer do that latencytop cannot already do?


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