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    SubjectRe: [GIT PULL] adaptive spinning mutexes

    * Ingo Molnar <mingo@elte.hu> wrote:

    > Latest performance figures, on a 2-socket 16-way Nehalem test-system,
    > running the code above, measured via "test-mutex V 128 10" VFS
    > creat+unlink scalability test on tmpfs and ext3:
    >
    > no-spin spin
    >
    > [tmpfs] avg ops/sec: 291038 392865 (+34.9%)
    > [ext3] avg ops/sec: 283291 435674 (+53.7%)

    Btw., for historic kicks i just went back to v2.6.15-2019-gf17578d - the
    last pre-mutexes semaphore based kernel, using the same .config.

    I tracked down two bugs in it to make it boot on a Nehalem, so we can now
    compare the above numbers against historic semaphore performance:

    [v2.6.14] [v2.6.29]

    Semaphores | Mutexes
    ----------------------------------------------
    | no-spin spin
    |
    [tmpfs] ops/sec: 50713 | 291038 392865 (+34.9%)
    [ext3] ops/sec: 45214 | 283291 435674 (+53.7%)

    A 10x macro-performance improvement on ext3, compared to 2.6.14 :-)

    While lots of other details got changed meanwhile, i'm sure most of the
    performance win on this particular VFS workload comes from mutexes.

    So i think the long mutex migration pain was definitely worth it.

    Ingo


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