Re: REGRESSION: Performance regressions from switchinganon_vma->lock to mutex

From: Andi Kleen
Date: Fri Jun 17 2011 - 15:42:01 EST

On Fri, Jun 17, 2011 at 09:46:00AM -0700, Linus Torvalds wrote:
> On Fri, Jun 17, 2011 at 4:28 AM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> >
> > Something like so? Compiles and runs the benchmark in question.
> Oh, and can you do this with a commit log and sign-off, and I'll put
> it in my "anon_vma-locking" branch that I have. I'm not going to
> actually merge that branch into mainline until I've seen a few more
> acks or more testing by Tim.
> But if Tim's numbers hold up (-32% to +15% performance by just the
> first one, and +15% isn't actually an improvement since tmpfs
> read-ahead should have gotten us to +66%), I think we have to do this
> just to avoid the performance regression.

You could also add the mutex "optimize caching protocol"
patch I posted earlier to that branch.

It didn't actually improve Tim's throughput number, but it made the CPU
consumption of the mutex go down.