* [PATCH] sched/fair: Do not set skip buddy up the sched hierarchy @ 2019-10-31 18:45 Josh Don 2019-11-04 14:54 ` Vincent Guittot 0 siblings, 1 reply; 3+ messages in thread From: Josh Don @ 2019-10-31 18:45 UTC (permalink / raw) To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot Cc: Dietmar Eggemann, Steven Rostedt, Ben Segall, Paul Turner, Mel Gorman, linux-kernel, Venkatesh Pallipadi, Josh Don 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> --- kernel/sched/fair.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 682a754ea3e1..52ab06585d7f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6647,8 +6647,15 @@ 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; } /* -- 2.23.0.700.g56cf767bdb-goog ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] sched/fair: Do not set skip buddy up the sched hierarchy 2019-10-31 18:45 [PATCH] sched/fair: Do not set skip buddy up the sched hierarchy Josh Don @ 2019-11-04 14:54 ` Vincent Guittot 2019-11-06 22:14 ` [PATCH v2] " Josh Don 0 siblings, 1 reply; 3+ messages in thread From: Vincent Guittot @ 2019-11-04 14:54 UTC (permalink / raw) To: Josh Don Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Dietmar Eggemann, Steven Rostedt, Ben Segall, Paul Turner, Mel Gorman, linux-kernel, Venkatesh Pallipadi On Thu, 31 Oct 2019 at 19:45, Josh Don <joshdon@google.com> wrote: > > 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> > --- > kernel/sched/fair.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 682a754ea3e1..52ab06585d7f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6647,8 +6647,15 @@ 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; > } You should also update __clear_buddies_skip to only clear this skip > > /* > -- > 2.23.0.700.g56cf767bdb-goog > ^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH v2] sched/fair: Do not set skip buddy up the sched hierarchy 2019-11-04 14:54 ` Vincent Guittot @ 2019-11-06 22:14 ` Josh Don 0 siblings, 0 replies; 3+ messages in thread From: Josh Don @ 2019-11-06 22:14 UTC (permalink / raw) To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot Cc: Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman, linux-kernel, Paul Turner, Josh Don 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 ^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-11-06 22:14 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-10-31 18:45 [PATCH] sched/fair: Do not set skip buddy up the sched hierarchy Josh Don 2019-11-04 14:54 ` Vincent Guittot 2019-11-06 22:14 ` [PATCH v2] " Josh Don
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.