Messages in this thread | | | Date | Fri, 20 Apr 2007 23:58:32 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH] lazy freeing of memory through MADV_FREE |
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Eric Dumazet wrote: > Rik van Riel a écrit : >> Andrew Morton wrote: >>> On Fri, 20 Apr 2007 17:38:06 -0400 >>> Rik van Riel <riel@redhat.com> wrote: >>> >>>> Andrew Morton wrote: >>>> >>>>> I've also merged Nick's "mm: madvise avoid exclusive mmap_sem". >>>>> >>>>> - Nick's patch also will help this problem. It could be that your >>>>> patch >>>>> no longer offers a 2x speedup when combined with Nick's patch. >>>>> >>>>> It could well be that the combination of the two is even better, >>>>> but it >>>>> would be nice to firm that up a bit. >>>> I'll test that. >>> >>> Thanks. >> >> Well, good news. >> >> It turns out that Nick's patch does not improve peak >> performance much, but it does prevent the decline when >> running with 16 threads on my quad core CPU! >> >> We _definately_ want both patches, there's a huge benefit >> in having them both. >> >> Here are the transactions/seconds for each combination: >> >> vanilla new glibc madv_free kernel madv_free + mmap_sem >> threads >> >> 1 610 609 596 545 > > 545 tps versus 610 tps for one thread ? It seems quite bad, no ? > > Could you please find an explanation for this ?
I have no idea why this happens. Especially the last one, going from a write lock to a read lock on the mmap_sem should not make ANY difference whatsoever since we're running single threaded!
>> 2 1032 1136 1196 1200 >> 4 1070 1128 2014 2024 >> 8 1000 1088 1665 2087 >> 16 779 1073 1310 1999
Performance with 2 database threads is way better though, and performance with 4 or more threads more than doubles...
If you have an explanation on why single threaded performance went down a little on my quad core system, please let me know.
Does performance suffer at all on a real UP system?
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