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    SubjectRe: Scheduler benchmarks - a follow-up

    * Rob Hussey <robjhussey@gmail.com> wrote:

    > http://www.healthcarelinen.com/misc/benchmarks/BOUND_hackbench_benchmark2.png

    heh - am i the only one impressed by the consistency of the blue line in
    this graph? :-) [ and the green line looks a bit like a .. staircase? ]

    i've meanwhile tested hackbench 90 and the performance difference
    between -ck and -cfs-devel seems to be mostly down to the more precise
    (but slower) sched_clock() introduced in v2.6.23 and to the startup
    penalty of freshly created tasks.

    Putting back the 2.6.22 version and tweaking the startup penalty gives
    this:

    [hackbench 90, smaller is better]

    sched-devel.git sched-devel.git+lowres-sched-clock+dsp
    --------------- --------------------------------------
    5.555 5.149
    5.641 5.149
    5.572 5.171
    5.583 5.155
    5.532 5.111
    5.540 5.138
    5.617 5.176
    5.542 5.119
    5.587 5.159
    5.553 5.177
    --------------------------------------
    avg: 5.572 avg: 5.150 (-8.1%)

    ('lowres-sched-clock' is the patch i sent in the previous mail. 'dsp' is
    a disable-startup-penalty patch that is in the latest sched-devel.git)

    i have used your .config to conduct this test.

    can you reproduce this with the (very-) latest sched-devel git tree:

    git-pull git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched-devel.git

    plus with the low-res-sched-clock patch (re-) attached below?

    Ingo
    ---
    arch/i386/kernel/tsc.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    Index: linux/arch/i386/kernel/tsc.c
    ===================================================================
    --- linux.orig/arch/i386/kernel/tsc.c
    +++ linux/arch/i386/kernel/tsc.c
    @@ -110,9 +110,9 @@ unsigned long long native_sched_clock(vo
    * very important for it to be as fast as the platform
    * can achive it. )
    */
    - if (unlikely(!tsc_enabled && !tsc_unstable))
    + if (1 || unlikely(!tsc_enabled && !tsc_unstable))
    /* No locking but a rare wrong value is not a big deal: */
    - return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
    + return jiffies_64 * (1000000000 / HZ);

    /* read the Time Stamp Counter: */
    rdtscll(this_offset);
    -
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