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

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Message-Id: <1223838786.8634.8.camel@lappy.programming.kicks-ass.net>
Date:	Sun, 12 Oct 2008 21:13:06 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Török Edwin <edwintorok@...il.com>
Cc:	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 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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