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    Subject[sched, patch] better wake-balancing

    another approach would be the patch below, to do wakeup-balancing only
    if the wakeup CPU or the task CPU is idle.

    I've measured half-loaded tbench and unless total wakeup-balancing
    removal it does not degrade with this patch applied, while fully loaded
    tbench and other workloads clearly improve.

    Ken, could you give this one a try? (It's against the current scheduler
    queue in -mm, but also applies fine to current Linus trees.)



    do wakeup-balancing only if the wakeup-CPU or the task-CPU is idle.

    this prevents excessive wakeup-balancing while the system is highly
    loaded, but helps spread out the workload on partly idle systems.

    Signed-off-by: Ingo Molnar <>

    kernel/sched.c | 6 ++++++
    1 files changed, 6 insertions(+)

    Index: linux-sched-curr/kernel/sched.c
    --- linux-sched-curr.orig/kernel/sched.c
    +++ linux-sched-curr/kernel/sched.c
    @@ -1252,7 +1252,13 @@ static int try_to_wake_up(task_t *p, uns
    if (unlikely(task_running(rq, p)))
    goto out_activate;

    + /*
    + * If neither this CPU, nor the previous CPU the task was
    + * running on is idle then skip wakeup-balancing:
    + */
    new_cpu = cpu;
    + if (!idle_cpu(this_cpu) && !idle_cpu(cpu))
    + goto out_set_cpu;

    schedstat_inc(rq, ttwu_cnt);
    if (cpu == this_cpu) {
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      Last update: 2005-07-29 16:18    [W:0.027 / U:3.688 seconds]
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