Messages in this thread |  | | From | Vincent Guittot <> | Date | Thu, 26 Dec 2019 16:05:46 +0100 | Subject | Re: [PATCH v3] sched/fair: Do not set skip buddy up the sched hierarchy |
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On Thu, 19 Dec 2019 at 01:14, Josh Don <joshdon@google.com> wrote: > > From: Venkatesh Pallipadi <venki@google.com> > > Setting the skip buddy up the hierarchy effectively means that a thread > calling yield will also end up skipping the other tasks in its hierarchy > as well. However, a yielding thread shouldn't end up causing this > behavior on behalf of its entire hierarchy. > > For typical uses of yield, setting the skip buddy 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. > > Co-developed-by: Josh Don <joshdon@google.com> > Signed-off-by: Josh Don <joshdon@google.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> --- > v2: Only clear skip buddy on the current cfs_rq > > v3: Modify comment describing the justification for this change. > > kernel/sched/fair.c | 15 ++++++++------- > 1 file changed, 8 insertions(+), 7 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e97a01..0056b57d52cb 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4051,13 +4051,10 @@ static void __clear_buddies_next(struct sched_entity *se) > > static 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) > @@ -6552,8 +6549,12 @@ 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; > + /* > + * Only set the skip buddy for the task requesting it. Setting the skip > + * buddy up the hierarchy would result in skipping all other tasks in > + * the hierarchy as well. > + */ > + cfs_rq_of(se)->skip = se; > } > > /* > -- > 2.24.1.735.g03f4e72817-goog >
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