Re: [PATCH] lock stat for -rt 2.6.20-rc2-rt2.2.lock_stat.patch

[Bill Huey (hui) <billh@gnuppy.monkey.org>]

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