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    SubjectRe: [PATCH] sched, numa: migrates_degrades_locality()
    On Thu, Jul 25, 2013 at 12:40:09PM +0200, Peter Zijlstra wrote:
    >
    > Subject: sched, numa: migrates_degrades_locality()
    > From: Peter Zijlstra <peterz@infradead.org>
    > Date: Mon Jul 22 14:02:54 CEST 2013
    >
    > It just makes heaps of sense; so add it and make both it and
    > migrate_improve_locality() a sched_feat().
    >

    Ok. I'll be splitting this patch and merging part of it into "sched:
    Favour moving tasks towards the preferred node" and keeping the
    degrades_locality as a separate patch. I'm also not a fan of the
    tunables names NUMA_FAULTS_UP and NUMA_FAULTS_DOWN because it is hard to
    guess what they mean. NUMA_FAVOUR_HIGHER, NUMA_RESIST_LOWER?

    Change to just the parent patch looks is as follows. task_faults() is
    not introduced yet in the series which is why it is still missing.

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 78bfbea..5ea3afe 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -3978,8 +3978,10 @@ static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
    {
    int src_nid, dst_nid;

    - if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
    + if (!sched_feat(NUMA_FAVOUR_HIGHER || !p->numa_faults ||
    + !(env->sd->flags & SD_NUMA))) {
    return false;
    + }

    src_nid = cpu_to_node(env->src_cpu);
    dst_nid = cpu_to_node(env->dst_cpu);
    @@ -3988,7 +3990,7 @@ static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
    p->numa_migrate_seq >= sysctl_numa_balancing_settle_count)
    return false;

    - if (p->numa_preferred_nid == dst_nid)
    + if (p->numa_faults[dst_nid] > p->numa_faults[src_nid])
    return true;

    return false;
    diff --git a/kernel/sched/features.h b/kernel/sched/features.h
    index 99399f8..97a1136 100644
    --- a/kernel/sched/features.h
    +++ b/kernel/sched/features.h
    @@ -69,4 +69,11 @@ SCHED_FEAT(LB_MIN, false)
    #ifdef CONFIG_NUMA_BALANCING
    SCHED_FEAT(NUMA, false)
    SCHED_FEAT(NUMA_FORCE, false)
    +
    +/*
    + * NUMA_FAVOUR_HIGHER will favor moving tasks towards nodes where a
    + * higher number of hinting faults are recorded during active load
    + * balancing.
    + */
    +SCHED_FEAT(NUMA_FAVOUR_HIGHER, true)
    #endif
    --
    Mel Gorman
    SUSE Labs


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