Messages in this thread | | | Subject | Re: [PATCH -v9][RFC] mutex: implement adaptive spinning | From | Chris Mason <> | Date | Tue, 13 Jan 2009 21:58:19 -0500 |
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On Tue, 2009-01-13 at 18:21 +0100, Peter Zijlstra wrote: > On Tue, 2009-01-13 at 08:49 -0800, Linus Torvalds wrote: > > > > So do a v10, and ask people to test. > > --- > Subject: mutex: implement adaptive spinning > From: Peter Zijlstra <a.p.zijlstra@chello.nl> > Date: Mon Jan 12 14:01:47 CET 2009 > > Change mutex contention behaviour such that it will sometimes busy wait on > acquisition - moving its behaviour closer to that of spinlocks. >
I've spent a bunch of time on this one, and noticed earlier today that I still had bits of CONFIG_FTRACE compiling. I wasn't actually tracing anything, but it seems to have had a big performance hit.
The bad news is the simple spin got much much faster, dbench 50 coming in at 1282MB/s instead of 580MB/s. (other benchmarks give similar results)
v10 is better that not spinning, but its in the 5-10% range. So, I've been trying to find ways to close the gap, just to understand exactly where it is different.
If I take out: /* * If there are pending waiters, join them. */ if (!list_empty(&lock->wait_list)) break;
v10 pops dbench 50 up to 1800MB/s. The other tests soundly beat my spinning and aren't less fair. But clearly this isn't a good solution.
I tried a few variations, like only checking the wait list once before looping, which helps some. Are there other suggestions on better tuning options?
(I retested v7 and see similar results)
-chris
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