Re: [GIT PULL] adaptive spinning mutexes

Ingo Molnar
2009-01-15T18:06:19Z

* Matthew Wilcox <matthew@wil.cx> 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