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Date:	Thu, 4 Jan 2007 00:12:50 -0800
From:	Bill Huey (hui) <billh@...ppy.monkey.org>
To:	"Chen, Tim C" <tim.c.chen@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Walker <dwalker@...sta.com>,
	"Bill Huey (hui)" <billh@...ppy.monkey.org>
Subject: Re: [PATCH] lock stat for -rt 2.6.20-rc2-rt2.2.lock_stat.patch

On Wed, Jan 03, 2007 at 06:14:11PM -0800, Chen, Tim C wrote:
> Bill Huey (hui) wrote:
> http://mmlinux.sf.net/public/patch-2.6.20-rc2-rt2.3.lock_stat.patch
> > If you can rerun it and post the results, it'll hopefully show the
> > behavior of that lock acquisition better.
> 
> Here's the run with fix to produce correct statistics.
> 
> Tim
> 
> @contention events = 848858
> @failure_events = 10
> @lookup_failed_scope = 175
> @lookup_failed_static = 47
> @static_found = 17
...
> [112584, 150, 6 -- 256, 0]              {init, kernel/futex.c, 2781}
> [597012, 183895, 136277 -- 9546, 0]             {mm_init, kernel/fork.c,
> 369}

Interesting. The second column means that those can be adaptively spun
on to prevent the blocking from happening. That's roughly 1/3rd of the
blocking events that happen (second/first). Something like that would
help out, but the problem is that contention on that lock in the first
place.

Also, Linux can do a hell of a lot of context switches per second. Is
the number of total contentions (top figure) in that run consistent with
the performance degradation ? and how much the reduction of those events
by 1/3rd would help out with the benchmark ? Those are the questions in
my mind at this moment.

bill

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