Messages in this thread Patch in this message | | | Date | Wed, 6 Nov 2019 14:14:48 -0800 | Subject | [PATCH v2] sched/fair: Do not set skip buddy up the sched hierarchy | From | Josh Don <> |
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From: Venkatesh Pallipadi <venki@google.com>
Setting skip buddy all the way up the hierarchy does not play well with intra-cgroup yield. One typical usecase of yield is when a thread in a cgroup wants to yield CPU to another thread within the same cgroup. For such a case, setting the skip buddy all the way up the hierarchy is counter-productive, as that results in CPU being yielded to a task in some other cgroup.
So, limit the skip effect only to the task requesting it.
Signed-off-by: Josh Don <joshdon@google.com> --- Changelog since v1: - As an optimization, skip clearing the skip buddy up the hierarchy - Due to the above, it makes sense to inline __clear_buddies_skip; while we're at it, inline the other __clear_buddies* functions as well.
kernel/sched/fair.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 682a754ea3e1..dbac30e3cc08 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4010,7 +4010,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) } } -static void __clear_buddies_last(struct sched_entity *se) +static inline void __clear_buddies_last(struct sched_entity *se) { for_each_sched_entity(se) { struct cfs_rq *cfs_rq = cfs_rq_of(se); @@ -4021,7 +4021,7 @@ static void __clear_buddies_last(struct sched_entity *se) } } -static void __clear_buddies_next(struct sched_entity *se) +static inline void __clear_buddies_next(struct sched_entity *se) { for_each_sched_entity(se) { struct cfs_rq *cfs_rq = cfs_rq_of(se); @@ -4032,15 +4032,12 @@ static void __clear_buddies_next(struct sched_entity *se) } } -static void __clear_buddies_skip(struct sched_entity *se) +static inline void __clear_buddies_skip(struct sched_entity *se) { - for_each_sched_entity(se) { - struct cfs_rq *cfs_rq = cfs_rq_of(se); - if (cfs_rq->skip != se) - break; + struct cfs_rq *cfs_rq = cfs_rq_of(se); + if (cfs_rq->skip == se) cfs_rq->skip = NULL; - } } static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se) @@ -4051,8 +4048,7 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se) if (cfs_rq->next == se) __clear_buddies_next(se); - if (cfs_rq->skip == se) - __clear_buddies_skip(se); + __clear_buddies_skip(se); } static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq); @@ -6647,8 +6643,15 @@ static void set_next_buddy(struct sched_entity *se) static void set_skip_buddy(struct sched_entity *se) { - for_each_sched_entity(se) - cfs_rq_of(se)->skip = se; + /* + * One typical usecase of yield is when a thread in a cgroup + * wants to yield CPU to another thread within the same cgroup. + * For such a case, setting the skip buddy all the way up the + * hierarchy is counter-productive, as that results in CPU being + * yielded to a task in some other cgroup. So, only set skip + * for the task requesting it. + */ + cfs_rq_of(se)->skip = se; } /* -- 2.24.0.rc1.363.gb1bccd3e3d-goog
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