Messages in this thread | | | Date | Mon, 29 Apr 2019 15:13:01 +0800 | From | Aaron Lu <> | Subject | Re: [RFC PATCH v2 13/17] sched: Add core wide task selection and scheduling. |
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On Tue, Apr 23, 2019 at 04:18:18PM +0000, Vineeth Remanan Pillai wrote: > +// XXX fairness/fwd progress conditions > +static struct task_struct * > +pick_task(struct rq *rq, const struct sched_class *class, struct task_struct *max) > +{ > + struct task_struct *class_pick, *cookie_pick; > + unsigned long cookie = 0UL; > + > + /* > + * We must not rely on rq->core->core_cookie here, because we fail to reset > + * rq->core->core_cookie on new picks, such that we can detect if we need > + * to do single vs multi rq task selection. > + */ > + > + if (max && max->core_cookie) { > + WARN_ON_ONCE(rq->core->core_cookie != max->core_cookie); > + cookie = max->core_cookie; > + } > + > + class_pick = class->pick_task(rq); > + if (!cookie) > + return class_pick; > + > + cookie_pick = sched_core_find(rq, cookie); > + if (!class_pick) > + return cookie_pick; > + > + /* > + * If class > max && class > cookie, it is the highest priority task on > + * the core (so far) and it must be selected, otherwise we must go with > + * the cookie pick in order to satisfy the constraint. > + */ > + if (cpu_prio_less(cookie_pick, class_pick) && core_prio_less(max, class_pick))
It apapears to me the cpu_prio_less(cookie_pick, class_pick) isn't needed.
If cookie_pick is idle task, then cpu_prio_less(cookie_pick, class_pick) is always true; If cookie_pick is not idle task and has the same sched class as class_pick, then class_pick is the best candidate to run accoring to their sched class. In this case, cpu_prio_less(cookie_pick, class_pick) shouldn't return false or it feels like a bug; If cookie_pick is not idle task and has a different sched class as class_pick: - if cookie_pick's sched class has higher priority than class_pick's sched class, then cookie_pick should have been selected in previous sched class iteration; and since its cookie matches with max, everything should have been finished already; - if cookie_pick's sched class has lower priority than class_pick's sched class, then cpu_prio_less(cookie_pick, class_pick) will still returns true.
So looks like cpu_prio_less(cookie_pick, class_pick) should always return true and thus not needed.
> + return class_pick; > + > + return cookie_pick; > +}
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