Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 30 Jan 2014 13:56:28 +0100 | Subject | Re: [PATCH 7/9] sched/fair: Optimize cgroup pick_next_task_fair |
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On 30 January 2014 13:37, Peter Zijlstra <peterz@infradead.org> wrote: > On Thu, Jan 30, 2014 at 01:18:09PM +0100, Vincent Guittot wrote: >> On 28 January 2014 18:16, Peter Zijlstra <peterz@infradead.org> wrote: >> >> [snip] >> >> > >> > @@ -4662,9 +4682,86 @@ static void check_preempt_wakeup(struct >> > static struct task_struct * >> > pick_next_task_fair(struct rq *rq, struct task_struct *prev) >> > { >> > - struct task_struct *p; >> > struct cfs_rq *cfs_rq = &rq->cfs; >> > struct sched_entity *se; >> > + struct task_struct *p; >> > + >> > +#ifdef CONFIG_FAIR_GROUP_SCHED >> > + if (!cfs_rq->nr_running) >> > + return NULL; >> >> Couldn't you move the test above out of the CONFIG_FAIR_GROUP_SCHED >> and remove the same test that is done after the simple label > > No, we have to check it twice because.. >> >> > + >> > + if (prev->sched_class != &fair_sched_class) >> > + goto simple; >> > + >> > + /* >> > + * Because of the set_next_buddy() in dequeue_task_fair() it is rather >> > + * likely that a next task is from the same cgroup as the current. >> > + * >> > + * Therefore attempt to avoid putting and setting the entire cgroup >> > + * hierarchy, only change the part that actually changes. >> > + */ >> > + >> > + do { >> > + struct sched_entity *curr = cfs_rq->curr; >> > + >> > + /* >> > + * Since we got here without doing put_prev_entity() we also >> > + * have to consider cfs_rq->curr. If it is still a runnable >> > + * entity, update_curr() will update its vruntime, otherwise >> > + * forget we've ever seen it. >> > + */ >> > + if (curr && curr->on_rq) >> > + update_curr(cfs_rq); >> > + else >> > + curr = NULL; >> > + >> > + /* >> > + * This call to check_cfs_rq_runtime() will do the throttle and >> > + * dequeue its entity in the parent(s). Therefore the 'simple' >> > + * nr_running test will indeed be correct. >> > + */ >> > + if (unlikely(check_cfs_rq_runtime(cfs_rq))) >> > + goto simple; > > ... here if you read the comment above, we could have modified the > nr_running.
ok, i missed this point
> >> > + se = pick_next_entity(cfs_rq, curr); >> > + cfs_rq = group_cfs_rq(se); >> > + } while (cfs_rq); >> > + >> > + p = task_of(se); >> > + >> > + /* >> > + * Since we haven't yet done put_prev_entity and if the selected task >> > + * is a different task than we started out with, try and touch the >> > + * least amount of cfs_rqs. >> > + */ >> > + if (prev != p) { >> > + struct sched_entity *pse = &prev->se; >> > + >> > + while (!(cfs_rq = is_same_group(se, pse))) { >> > + int se_depth = se->depth; >> > + int pse_depth = pse->depth; >> > + >> > + if (se_depth <= pse_depth) { >> > + put_prev_entity(cfs_rq_of(pse), pse); >> > + pse = parent_entity(pse); >> > + } >> > + if (se_depth >= pse_depth) { >> > + set_next_entity(cfs_rq_of(se), se); >> > + se = parent_entity(se); >> > + } >> > + } >> > + >> > + put_prev_entity(cfs_rq, pse); >> > + set_next_entity(cfs_rq, se); >> > + } >> > + >> > + if (hrtick_enabled(rq)) >> > + hrtick_start_fair(rq, p); >> > + >> > + return p; >> > +simple: >> > + cfs_rq = &rq->cfs; >> > +#endif >> > >> > if (!cfs_rq->nr_running) >> > return NULL; > > And therefore this test needs to stay.
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