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

Tim Chen
2011-06-16T20:25:42Z

On Wed, 2011-06-15 at 18:50 -0700, Linus Torvalds wrote:

>
> Tim, have you tried running your bigger load with that patch? You
> could try my patch on top too just to match Peter's tree, but I doubt
> that's the big first-order issue.
>
> Linus

I ran exim with different kernel versions. Using 2.6.39-vanilla
kernel as a baseline, the results are as follow:

Throughput
2.6.39(vanilla) 100.0%
2.6.39+ra-patch 166.7% (+66.7%) (note: tmpfs readahead patchset is merged in 3.0-rc2)
3.0-rc2(vanilla) 68.0% (-32%)
3.0-rc2+linus 115.7% (+15.7%)
3.0-rc2+linus+softirq 86.2% (-17.3%)

So Linus' patch certainly helped things over vanilla 3.0-rc2, but throughput is still
less than the 2.6.39 with the readahead patch set. The softirq patch I used was from Ingo's
combined patch from Shaohua and Paul. It seems odd that it makes things worse. I will
recheck this data probably just this patch and without Linus' patch later.

I also notice that the run to run variations have increased quite a bit for 3.0-rc2.
I'm using 6 runs per kernel. Perhaps a side effect of converting the anon_vma->lock to mutex?

(Max-Min)/avg
2.6.39(vanilla) 3%
2.6.39+ra-patch 3%
3.0-rc2(vanilla) 20%
3.0-rc2+linus 36%
3.0-rc2+linus+softirq 40%

Thanks.

Tim