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    Subject[tip:sched/core] sched: Cleanup select_task_rq_fair()
    Commit-ID:  a50bde5130f65733142b32975616427d0ea50856
    Gitweb: http://git.kernel.org/tip/a50bde5130f65733142b32975616427d0ea50856
    Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
    AuthorDate: Thu, 12 Nov 2009 15:55:28 +0100
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Fri, 13 Nov 2009 10:09:58 +0100

    sched: Cleanup select_task_rq_fair()

    Clean up the new affine to idle sibling bits while trying to
    grok them. Should not have any function differences.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Mike Galbraith <efault@gmx.de>
    LKML-Reference: <20091112145610.832503781@chello.nl>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/sched_fair.c | 73 +++++++++++++++++++++++++++++++++++---------------
    1 files changed, 51 insertions(+), 22 deletions(-)

    diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
    index e4d4483..a32df15 100644
    --- a/kernel/sched_fair.c
    +++ b/kernel/sched_fair.c
    @@ -1319,6 +1319,41 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
    }

    /*
    + * Try and locate an idle CPU in the sched_domain.
    + */
    +static int
    +select_idle_sibling(struct task_struct *p, struct sched_domain *sd, int target)
    +{
    + int cpu = smp_processor_id();
    + int prev_cpu = task_cpu(p);
    + int i;
    +
    + /*
    + * If this domain spans both cpu and prev_cpu (see the SD_WAKE_AFFINE
    + * test in select_task_rq_fair) and the prev_cpu is idle then that's
    + * always a better target than the current cpu.
    + */
    + if (target == cpu) {
    + if (!cpu_rq(prev_cpu)->cfs.nr_running)
    + target = prev_cpu;
    + }
    +
    + /*
    + * Otherwise, iterate the domain and find an elegible idle cpu.
    + */
    + if (target == -1 || target == cpu) {
    + for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
    + if (!cpu_rq(i)->cfs.nr_running) {
    + target = i;
    + break;
    + }
    + }
    + }
    +
    + return target;
    +}
    +
    +/*
    * sched_balance_self: balance the current task (running on cpu) in domains
    * that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
    * SD_BALANCE_EXEC.
    @@ -1373,36 +1408,30 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
    }

    if (want_affine && (tmp->flags & SD_WAKE_AFFINE)) {
    - int candidate = -1, i;
    + int target = -1;

    + /*
    + * If both cpu and prev_cpu are part of this domain,
    + * cpu is a valid SD_WAKE_AFFINE target.
    + */
    if (cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
    - candidate = cpu;
    + target = cpu;

    /*
    - * Check for an idle shared cache.
    + * If there's an idle sibling in this domain, make that
    + * the wake_affine target instead of the current cpu.
    + *
    + * XXX: should we possibly do this outside of
    + * WAKE_AFFINE, in case the shared cache domain is
    + * smaller than the WAKE_AFFINE domain?
    */
    - if (tmp->flags & SD_PREFER_SIBLING) {
    - if (candidate == cpu) {
    - if (!cpu_rq(prev_cpu)->cfs.nr_running)
    - candidate = prev_cpu;
    - }
    -
    - if (candidate == -1 || candidate == cpu) {
    - for_each_cpu(i, sched_domain_span(tmp)) {
    - if (!cpumask_test_cpu(i, &p->cpus_allowed))
    - continue;
    - if (!cpu_rq(i)->cfs.nr_running) {
    - candidate = i;
    - break;
    - }
    - }
    - }
    - }
    + if (tmp->flags & SD_PREFER_SIBLING)
    + target = select_idle_sibling(p, tmp, target);

    - if (candidate >= 0) {
    + if (target >= 0) {
    affine_sd = tmp;
    want_affine = 0;
    - cpu = candidate;
    + cpu = target;
    }
    }


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