Messages in this thread | | | Date | Fri, 5 Feb 2021 11:37:31 -0500 | From | Joel Fernandes <> | Subject | Re: [PATCH v10 2/5] sched: CGroup tagging interface for core scheduling |
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On Thu, Feb 04, 2021 at 03:52:53PM +0100, Peter Zijlstra wrote: > On Fri, Jan 22, 2021 at 08:17:01PM -0500, Joel Fernandes (Google) wrote: > > +static void sched_core_update_cookie(struct task_struct *p, unsigned long cookie, > > + enum sched_core_cookie_type cookie_type) > > +{ > > + struct rq_flags rf; > > + struct rq *rq; > > + > > + if (!p) > > + return; > > + > > + rq = task_rq_lock(p, &rf); > > + > > + switch (cookie_type) { > > + case sched_core_task_cookie_type: > > + p->core_task_cookie = cookie; > > + break; > > + case sched_core_group_cookie_type: > > + p->core_group_cookie = cookie; > > + break; > > + default: > > + WARN_ON_ONCE(1); > > + } > > + > > + /* Set p->core_cookie, which is the overall cookie */ > > + __sched_core_update_cookie(p); > > + > > + if (sched_core_enqueued(p)) { > > + sched_core_dequeue(rq, p); > > + if (!p->core_cookie) { > > + task_rq_unlock(rq, p, &rf); > > + return; > > + } > > + } > > + > > + if (sched_core_enabled(rq) && > > + p->core_cookie && task_on_rq_queued(p)) > > + sched_core_enqueue(task_rq(p), p); > > + > > + /* > > + * If task is currently running or waking, it may not be compatible > > + * anymore after the cookie change, so enter the scheduler on its CPU > > + * to schedule it away. > > + */ > > + if (task_running(rq, p) || p->state == TASK_WAKING) > > + resched_curr(rq); > > I'm not immediately seeing the need for that WAKING test. Since we're > holding it's rq->lock, the only place that task can be WAKING is on the > wake_list. And if it's there, it needs to acquire rq->lock to get > enqueued, and rq->lock again to get scheduled. > > What am I missing?
Hi Peter,
I did this way following a similar pattern in affine_move_task(). However, I think you are right. Unlike in the case affine_move_task(), we have schedule() to do the right thing for us in case of any races with wakeup. So the TASK_WAKING test is indeed not needed and we can drop tha test. Apologies for adding the extra test out of paranoia.
thanks,
- Joel
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