Re: [GIT PULL] adaptive spinning mutexes

[Ingo Molnar]

* Matthew Wilcox <matthew@xxxxxx> wrote:

> On Wed, Jan 14, 2009 at 08:28:11PM +0100, Ingo Molnar wrote:
> >                       [v2.6.14]     [v2.6.29]
> > 
> >                       Semaphores  | Mutexes
> >             ----------------------------------------------
> >                                   | no-spin           spin
> >                                   |
> >   [tmpfs]   ops/sec:       50713  |  291038         392865       (+34.9%)
> >   [ext3]    ops/sec:       45214  |  283291         435674       (+53.7%)
> > 
> > A 10x macro-performance improvement on ext3, compared to 2.6.14 :-)
> > 
> > While lots of other details got changed meanwhile, i'm sure most of 
> > the performance win on this particular VFS workload comes from 
> > mutexes.
> 
> I asked a couple of our benchmarking teams to try -v9.  Neither the OLTP 
> benchmark, nor the kernel-perf test suite found any significant 
> performance change.  I suspect mutex contention isn't a significant 
> problem for most workloads.

basically only VFS is mutex-bound really, and few of the 'benchmarks' tend 
to be VFS intense. Maybe things like mail-server benchmarks would do that.

Also, -v9 is like two days old code ;-) Old and crufty. The real 
performance uptick was not even in -v10 but in -v11 (the one we submitted 
in this thread).

	Ingo
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