Re: [PATCH -v8][RFC] mutex: implement adaptive spinning

Peter Zijlstra
2009-01-12T16:50:15Z

On Mon, 2009-01-12 at 11:45 -0500, Chris Mason wrote:
> On Mon, 2009-01-12 at 08:20 -0800, Linus Torvalds wrote:
> >
> > On Mon, 12 Jan 2009, Linus Torvalds wrote:
> > >
> > > You made it back into the locked version.
> >
> > Btw, even if you probably had some reason for this, one thing to note is
> > that I think Chris' performance testing showed that the version using a
> > lock was inferior to his local btrfs hack, while the unlocked version
> > actually beat his hack.
> >
>
> The spinning hack was faster than everything before v7 (we'll call it
> the Linus-fix), and the v7 code was much faster than my spin.
>
> This is somewhere in between, with slightly better fairness than v7.
>
> spin v7 v8
> dbench 50 580MB/s 789MB/s 421MB/s
> file creates 152 file/s 162 file/s 195 file/s
> file stat 3.8s total 2.3s total 5.3s total
>
> (the file stat run is total run time, so lower is better. The other
> numbers are files or MB per second, so higher is better)
>
> For the file create run, v8 had much lower system time than v7,
> averaging 1s of sys time per proc instead of 1.6s.

Right, how about the spread in completion time, because that is the only
reason I tried this fairness stuff, because you reported massive
differences there.