lkml.org 
[lkml]   [2007]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] SLUB use cmpxchg_local
    * Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca) wrote:
    > Ok, I played with your patch a bit, and the results are quite
    > interesting:
    >
    ...
    > Summary:
    >
    > (tests repeated 10000 times on a 3GHz Pentium 4)
    > (kernel DEBUG menuconfig options are turned off)
    > results are in cycles per iteration
    > I did 2 runs of the slab.git HEAD to have an idea of errors associated
    > to the measurements:
    >
    > | slab.git HEAD slub (min-max) | cmpxchg_local slub
    > kmalloc(8) | 190 - 201 | 83
    > kfree(8) | 351 - 351 | 363
    > kmalloc(64) | 224 - 245 | 115
    > kfree(64) | 389 - 394 | 397
    > kmalloc(16384)| 713 - 741 | 724
    > kfree(16384) | 843 - 856 | 843
    >
    > Therefore, there seems to be a repeatable gain on the kmalloc fast path
    > (more than twice faster). No significant performance hit for the kfree
    > case, but no gain neither, same for large kmalloc, as expected.
    >

    Having no performance improvement for kfree seems a little weird, since
    we are moving from irq disable to cmpxchg_local in the fast path. A
    possible explanation would be that we are always hitting the slow path.
    I did a simple test, counting the number of fast vs slow paths with my
    cmpxchg_local slub version:

    (initial state before the test)
    [ 386.359364] Fast slub free: 654982
    [ 386.369507] Slow slub free: 392195
    [ 386.379660] SLUB Performance testing
    [ 386.390361] ========================
    [ 386.401020] 1. Kmalloc: Repeatedly allocate then free test
    ...
    (after test 1)
    [ 387.366002] Fast slub free: 657338 diff (2356)
    [ 387.376158] Slow slub free: 482162 diff (89967)

    [ 387.386294] 2. Kmalloc: alloc/free test
    ...
    (after test 2)
    [ 387.897816] Fast slub free: 748968 (diff 91630)
    [ 387.907947] Slow slub free: 482584 diff (422)

    Therefore, in the test where we have separate passes for slub allocation
    and free, we hit mostly the slow path. Any particular reason for that ?

    Note that the alloc/free test (test 2) seems to hit the fast path as
    expected.

    Mathieu

    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-08-21 22:55    [W:0.023 / U:30.968 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site