Messages in this thread | | | Date | Thu, 30 Jan 2014 13:37:10 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 7/9] sched/fair: Optimize cgroup pick_next_task_fair |
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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.
> > + 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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