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    SubjectRe: hackbench regression due to commit 9dfc6e68bfe6e
    On Tue, 6 Apr 2010, Zhang, Yanmin wrote:

    > Thanks. I tried 2 and 4 times and didn't see much improvement.
    > I checked /proc/vamallocinfo and it doesn't have item of pcpu_get_vm_areas
    > when I use 4 times of PERCPU_DYNAMIC_RESERVE.

    > I used perf to collect dtlb misses and LLC misses. dtlb miss data is not
    > stable. Sometimes, we have a bigger dtlb miss, but get a better result.
    >
    > LLC misses data are more stable. Only LLC-load-misses is the clear sign now.
    > LLC-store-misses has no big difference.

    LLC-load-miss is exactly what condition?

    The cacheline environment in the hotpath should only include the following
    cache lines (without debugging and counters):

    1. The first cacheline from the kmem_cache structure

    (This is different from the sitation before the 2.6.34 changes. Earlier
    some critical values (object length etc) where available
    from the kmem_cache_cpu structure. The cacheline containing the percpu
    structure array was needed to determome the kmem_cache_cpu address!)

    2. The first cacheline from kmem_cache_cpu

    3. The first cacheline of the data object (free pointer)

    And in case of a kfree/ kmem_cache_free:

    4. Cacheline that contains the page struct of the page the object resides
    in.

    Can you post the .config you are using and the bootup messages?



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