Christoph Hellwig wrote:
On Thu, May 03, 2007 at 11:32:23AM +1000, Nick Piggin wrote:
The attached patch gets performance up a bit by avoiding some
barriers and some cachelines:
G5
pagefault fork exec
2.6.21 1.49-1.51 164.6-170.8 741.8-760.3
+patch 1.71-1.73 175.2-180.8 780.5-794.2
+patch2 1.61-1.63 169.8-175.0 748.6-757.0
So that brings the fork/exec hits down to much less than 5%, and
would likely speed up other things that lock the page, like write
or page reclaim.
Is that every fork/exec or just under certain cicumstances?
A 5% regression on every fork/exec is not acceptable.
Well after patch2, G5 fork is 3% and exec is 1%, I'd say the P4
numbers will be improved as well with that patch. Then if we have
specific lock/unlock bitops, I hope it should reduce that further.
The overhead that is there should just be coming from the extra
overhead in the file backed fault handler. For noop fork/execs,
I think that tends to be more pronounced, it is hard to see any
difference on any non-micro benchmark.
The other thing is that I think there could be some cache effects
happening -- for example the exec numbers on the 2nd line are
disproportionately large.
It definitely isn't a good thing to drop performance anywhere
though, so I'll keep looking for improvements.
--
SUSE Labs, Novell Inc.
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