Re: [GIT PULL] adaptive spinning mutexes

Matthew Wilcox
2009-01-15T17:44:40Z

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.

Has anyone found a non-synthetic benchmark where this makes a
significant difference? Aside from btrfs, I mean.

--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."