Re: [GIT PULL] adaptive spinning mutexes

[Matthew Wilcox]

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."
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