Re: REGRESSION: Performance regressions from switching anon_vma->lock to mutex

Tim Chen
2011-06-16T01:07:57Z

On Wed, 2011-06-15 at 23:37 +0200, Peter Zijlstra wrote:
> On Wed, 2011-06-15 at 14:12 -0700, Tim Chen wrote:
> > Thanks to Andi for providing the info. We've used this workaround in
> > our testing so it will not mask true kernel scaling bottlenecks.
>
>
> http://programming.kicks-ass.net/sekrit/39-2.txt.bz2
> http://programming.kicks-ass.net/sekrit/tip-2.txt.bz2
>
> tip+sirq+linus is still slightly faster than .39 here, although removing
> that sysconf() wreckage closed the gap considerably (needing to know the
> number of cpus to optimize locking sounds like a trainwreck all of its
> own, needing it _that_ often instead of just once at startup is even
> worse).
>

Peter,

Fengguang's readahead fixes for tmpfs removed another bottleneck before
anon_vma->lock become dominant. https://lkml.org/lkml/2011/4/26/143)
We've found this issue when we were testing exim earlier.
It was merged in 3.0-rc2 but not in plain 2.6.39. So with this patch on
2.6.39 we should get better comparison with 3.0-rc2.

Thanks.

Tim