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    SubjectRe: [PATCH]: 1/4 batch mark_page_accessed()
    Marcelo Tosatti wrote:
    > On Sun, Nov 21, 2004 at 06:44:04PM +0300, Nikita Danilov wrote:
    >>Batch mark_page_accessed() (a la lru_cache_add() and lru_cache_add_active()):
    >>page to be marked accessed is placed into per-cpu pagevec
    >>(page_accessed_pvec). When pagevec is filled up, all pages are processed in a
    >>This is supposed to decrease contention on zone->lru_lock.
    > Here are the STP 8way results:
    > 8way:


    > kernbench
    > Decreases performance significantly (on -j4 more notably), probably due to
    > the additional atomic operations as noted by Andrew:
    > kernel: nikita-b2 kernel: patch-2.6.10-rc2
    > Host: stp8-002 Host: stp8-003


    > Average Half Load -j 4 Run: Average Half Load -j 4 Run:
    > Elapsed Time 274.916 Elapsed Time 245.026
    > User Time 833.63 User Time 832.34
    > System Time 73.704 System Time 73.41
    > Percent CPU 335.8 Percent CPU 373.6
    > Context Switches 12984.8 Context Switches 13427.4
    > Sleeps 21459.2 Sleeps 21642

    Do you think looks like it may be a CPU scheduling or disk/fs artifact?
    Neither user nor system time are significantly worse, while the vanilla
    kernel is using a lot more of the CPUs' power (ie waiting for IO less,
    or becoming idle less often due to CPU scheduler balancing).

    Aside: under-load conditions like this is actually something where the
    CPU scheduler doesn't do brilliantly at currently. I attribute this to
    probably most "performance tests" loading it up as much as possible.
    I am (on and off) looking at improving performance in these conditions,
    and am making some inroads.
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