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    Subject[tip:sched/core] sched: call select_idle_sibling when not affine_sd
    Commit-ID:  b45cf72cf7e1dd3b4a95947f85659cfdc01dbdad
    Gitweb: http://git.kernel.org/tip/b45cf72cf7e1dd3b4a95947f85659cfdc01dbdad
    Author: Rik van Riel <riel@redhat.com>
    AuthorDate: Wed, 14 May 2014 11:40:37 -0400
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Mon, 19 May 2014 22:02:40 +0900

    sched: call select_idle_sibling when not affine_sd

    On smaller systems, the top level sched domain will be an affine
    domain, and select_idle_sibling is invoked for every SD_WAKE_AFFINE
    wakeup. This seems to be working well.

    On larger systems, with the node distance between far away NUMA nodes
    being > RECLAIM_DISTANCE, select_idle_sibling is only called if the
    waker and the wakee are on nodes less than RECLAIM_DISTANCE apart.

    This patch leaves in place the policy of not pulling the task across
    nodes on such systems, while fixing the issue that select_idle_sibling
    is not called at all in certain circumstances.

    The code will look for an idle CPU in the same CPU package as the
    CPU where the task ran previously.

    Cc: morten.rasmussen@arm.com
    Cc: mingo@kernel.org
    Cc: george.mccollister@gmail.com
    Cc: ktkhai@parallels.com
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
    Signed-off-by: Rik van Riel <riel@redhat.com>
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/20140514114037.2d93266f@annuminas.surriel.com
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    kernel/sched/fair.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index dd3fa14..429164d 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -4473,10 +4473,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
    sd = tmp;
    }

    - if (affine_sd) {
    - if (cpu != prev_cpu && wake_affine(affine_sd, p, sync))
    - prev_cpu = cpu;
    + if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync))
    + prev_cpu = cpu;

    + if (sd_flag & SD_BALANCE_WAKE) {
    new_cpu = select_idle_sibling(p, prev_cpu);
    goto unlock;
    }

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