Messages in this thread | | | Date | Thu, 03 May 2007 22:56:12 +1000 | From | Nick Piggin <> | Subject | Re: 2.6.22 -mm merge plans -- vm bugfixes |
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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.
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