linux-kernel - Re: [PATCH 0/7] lock contention tracking -v2

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Message-ID: <20070523215756.GA26450@gnuppy.monkey.org>
Date:	Wed, 23 May 2007 14:57:56 -0700
From:	Bill Huey (hui) <billh@...ppy.monkey.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Jason Baron <jbaron@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Christoph Hellwig <hch@...radead.org>,
	"Bill Huey (hui)" <billh@...ppy.monkey.org>
Subject: Re: [PATCH 0/7] lock contention tracking -v2

On Wed, May 23, 2007 at 12:33:11PM +0200, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
...
> > 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.
...
> 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)

per cpu is pretty important since you can potentially hit that logic more
often with your wait-time code. You don't want to effect the actual
measurement with the measurement code. It's that uncertainty principal thing.

It is looking pretty good. :) You might like to pretty the output even more,
but it's pretty usable as is.

bill

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