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    Subject[PATCH try 5] CFS: Add hierarchical tree-based penalty.
    Inspired by the recent change to BFS by Con Kolivas, this patch causes
    vruntime to be penalized based on parent depth from their root task
    group.

    I have, for the moment, decided to make it a default feature since the
    design of CFS ensures that broken applications depending on task enqueue
    behaviour behaving traditionally will continue to work.

    Signed-off-by: William Pitcock <nenolod@dereferenced.org>
    ---
    include/linux/sched.h | 2 ++
    kernel/sched.c | 4 ++++
    kernel/sched_fair.c | 8 ++++++++
    kernel/sched_features.h | 12 ++++++++++++
    4 files changed, 26 insertions(+), 0 deletions(-)

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 1e2a6db..3f0cff8 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -1494,6 +1494,8 @@ struct task_struct {
    unsigned long memsw_bytes; /* uncharged mem+swap usage */
    } memcg_batch;
    #endif
    +
    + int fork_depth;
    };

    /* Future-safe accessor for struct task_struct's cpus_allowed. */
    diff --git a/kernel/sched.c b/kernel/sched.c
    index dc85ceb..3fc3ebc 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -2621,6 +2621,10 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
    #endif

    rq = task_rq_lock(p, &flags);
    +
    + if (!(clone_flags & CLONE_THREAD))
    + p->fork_depth++;
    +
    activate_task(rq, p, 0);
    trace_sched_wakeup_new(p, 1);
    check_preempt_curr(rq, p, WF_FORK);
    diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
    index db3f674..a81acc5 100644
    --- a/kernel/sched_fair.c
    +++ b/kernel/sched_fair.c
    @@ -737,6 +737,14 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
    if (initial && sched_feat(START_DEBIT))
    vruntime += sched_vslice(cfs_rq, se);

    + if (sched_feat(HIERARCHICAL_PENALTY) &&
    + likely(entity_is_task(se))) {
    + struct task_struct *tsk = task_of(se);
    +
    + if (tsk->fork_depth > 1)
    + vruntime *= tsk->fork_depth;
    + }
    +
    /* sleeps up to a single latency don't count. */
    if (!initial) {
    unsigned long thresh = sysctl_sched_latency;
    diff --git a/kernel/sched_features.h b/kernel/sched_features.h
    index 83c66e8..cf17f97 100644
    --- a/kernel/sched_features.h
    +++ b/kernel/sched_features.h
    @@ -45,6 +45,18 @@ SCHED_FEAT(LAST_BUDDY, 1)
    SCHED_FEAT(CACHE_HOT_BUDDY, 1)

    /*
    + * Hierarchical tree-based penalty: penalize service deficit by
    + * an order of magnitude for each parent process in the process
    + * tree. This has the natural effect of forcing preference towards
    + * processes that are not fork()-hungry, like make(1), which helps
    + * to preserve good latency.
    + *
    + * This also has the side effect of providing in a limited way,
    + * per-user CPU entitlement partitioning.
    + */
    +SCHED_FEAT(HIERARCHICAL_PENALTY, 1)
    +
    +/*
    * Use arch dependent cpu power functions
    */
    SCHED_FEAT(ARCH_POWER, 0)
    --
    1.7.2.1


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