Date: Wed, 23 May 2007 12:33:11 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-kernel@vger.kernel.org, Bill Huey <billh@gnuppy.monkey.org>,
       Jason Baron <jbaron@redhat.com>, Steven Rostedt <rostedt@goodmis.org>,
       Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 0/7] lock contention tracking -v2
Message-ID: <20070523103311.GA13482@elte.hu>
References: <20070523072618.129001605@chello.nl>
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* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> Use the lockdep infrastructure to track lock contention and other lock 
> statistics.
> 
> It tracks lock contention events, and the first four unique call-sites 
> that encountered contention.
> 
> It also measures lock wait-time and hold-time in nanoseconds. The 
> minimum and maximum times are tracked, as well as a total (which 
> together with the number of event can give the avg).
> 
> All statistics are done per lock class, per write (exclusive state) 
> and per read (shared state).
> 
> The statistics are collected per-cpu, so that the collection overhead 
> is minimized via having no global cachemisses.
> 
> This new lock statistics feature is independent of the lock dependency 
> checking traditionally done by lockdep; it just shares the lock 
> tracking code. It is also possible to enable both and runtime disabled 
> either component - thereby avoiding the O(n^2) lock chain walks for 
> instance.

really nice changes! The wait-time and hold-time changes should make it 
as capable as lockmeter and more: lockmeter only measured spinlocks, 
while your approach covers all lock types (spinlocks, rwlocks and 
mutexes).

The performance enhancements in -v2 should make it much more scalable 
than your first version was. (in fact i think it should be completely 
scalable as the statistics counters are all per-cpu, so there should be 
no cacheline bouncing at all from this)

Also, you've detached it from CONFIG_PROVE_LOCKING so the 
lock-dependency overhead should be gone too.

Looks really good to me!

 Acked-by: Ingo Molnar <mingo@elte.hu>

	Ingo
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