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    Subject[tip:sched/core] sched/numa: Fix task or group comparison
    Commit-ID:  ca28aa53dd95868c9e38917b9881c09dacfacf1a
    Gitweb: http://git.kernel.org/tip/ca28aa53dd95868c9e38917b9881c09dacfacf1a
    Author: Rik van Riel <riel@redhat.com>
    AuthorDate: Mon, 7 Oct 2013 11:29:32 +0100
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Wed, 9 Oct 2013 14:48:08 +0200

    sched/numa: Fix task or group comparison

    This patch separately considers task and group affinities when
    searching for swap candidates during NUMA placement. If tasks
    are part of the same group, or no group at all, the task weights
    are considered.

    Some hysteresis is added to prevent tasks within one group from
    getting bounced between NUMA nodes due to tiny differences.

    If tasks are part of different groups, the code compares group
    weights, in order to favor grouping task groups together.

    The patch also changes the group weight multiplier to be the
    same as the task weight multiplier, since the two are no longer
    added up like before.

    Signed-off-by: Rik van Riel <riel@redhat.com>
    Signed-off-by: Mel Gorman <mgorman@suse.de>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/1381141781-10992-55-git-send-email-mgorman@suse.de
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/sched/fair.c | 32 +++++++++++++++++++++++++-------
    1 file changed, 25 insertions(+), 7 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 6f45461..423316c 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -962,7 +962,7 @@ static inline unsigned long group_weight(struct task_struct *p, int nid)
    if (!total_faults)
    return 0;

    - return 1200 * group_faults(p, nid) / total_faults;
    + return 1000 * group_faults(p, nid) / total_faults;
    }

    static unsigned long weighted_cpuload(const int cpu);
    @@ -1068,16 +1068,34 @@ static void task_numa_compare(struct task_numa_env *env,

    /*
    * If dst and source tasks are in the same NUMA group, or not
    - * in any group then look only at task weights otherwise give
    - * priority to the group weights.
    + * in any group then look only at task weights.
    */
    - if (!cur->numa_group || !env->p->numa_group ||
    - cur->numa_group == env->p->numa_group) {
    + if (cur->numa_group == env->p->numa_group) {
    imp = taskimp + task_weight(cur, env->src_nid) -
    task_weight(cur, env->dst_nid);
    + /*
    + * Add some hysteresis to prevent swapping the
    + * tasks within a group over tiny differences.
    + */
    + if (cur->numa_group)
    + imp -= imp/16;
    } else {
    - imp = groupimp + group_weight(cur, env->src_nid) -
    - group_weight(cur, env->dst_nid);
    + /*
    + * Compare the group weights. If a task is all by
    + * itself (not part of a group), use the task weight
    + * instead.
    + */
    + if (env->p->numa_group)
    + imp = groupimp;
    + else
    + imp = taskimp;
    +
    + if (cur->numa_group)
    + imp += group_weight(cur, env->src_nid) -
    + group_weight(cur, env->dst_nid);
    + else
    + imp += task_weight(cur, env->src_nid) -
    + task_weight(cur, env->dst_nid);
    }
    }


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