On Fri, Jun 06, 2014 at 02:59:56PM +0800, zhd...@sina.com wrote: > Hi all > > When computing cache hot, question-1: should we check the number of running > tasks > against the migration target runqueue, as shown by the following diff? > > It looks that we dont migrate task if it is buddy and the target cpu is not > idle. > > > --- a/kernel/sched/fair.c Fri Jun 6 12:37:37 2014 > +++ b/kernel/sched/fair.c Fri Jun 6 13:55:35 2014 > @@ -5051,7 +5050,7 @@ task_hot(struct task_struct *p, u64 now) > /* > * Buddy candidates are cache hot: > */ > - if (sched_feat(CACHE_HOT_BUDDY) && this_rq()->nr_running && > + if (sched_feat(CACHE_HOT_BUDDY) && env->dst_rq->nr_running && > (&p->se == cfs_rq_of(&p->se)->next || > &p->se == cfs_rq_of(&p->se)->last)) > return 1;
That is indeed the effective result for normal balancing, seeing how it pulls to the dst rq, and this_rq would be dst. This is of course false for a number of cases these days, most obviously the nohz idle balancing. > But based on the comment, question-2: should we check running tasks > against the runqueue of the given task? > --- a/kernel/sched/fair.c Fri Jun 6 12:37:37 2014 > +++ b/kernel/sched/fair.c Fri Jun 6 14:32:34 2014 > @@ -5051,7 +5051,7 @@ task_hot(struct task_struct *p, u64 now) > /* > * Buddy candidates are cache hot: > */ > - if (sched_feat(CACHE_HOT_BUDDY) && this_rq()->nr_running && > + if (sched_feat(CACHE_HOT_BUDDY) && task_rq(p)->nr_running && > (&p->se == cfs_rq_of(&p->se)->next || > &p->se == cfs_rq_of(&p->se)->last)) > return 1; That does appear to make more sense indeed, seeing how buddies are pairs of tasks, so protecting a lone task doesn't make sense. Mike, how did you intend this code to work?
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