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Date: Sun, 19 Jun 2011 16:33:32 +0800 From: Hillf Danton <dhillf@...il.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: LKML <linux-kernel@...r.kernel.org>, Mike Galbraith <efault@....de>, Yong Zhang <yong.zhang0@...il.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu> Subject: Re: [PATCH] sched: update cpupri for runqueue when its priority changes On Sun, Jun 19, 2011 at 1:11 AM, Steven Rostedt <rostedt@...dmis.org> wrote: >> There are two cases that NULL is returned in _pick_next_task_rt(), it is the >> second case, after checking rt_rq->rt_nr_running, that is captured, and if >> NULL is returned in the second case, the CPU priority does change. > > The two cases are: > > 1) no rt task exists > 2) the runqueue is throttled. > > We already talked about the throttled case. The case where no rt task > exists means that the last rt task has been dequeued. When that happens, > the cpupri is updated then. I don't see any bug. There's no need to > update cpupri at this point. > In case 2) , the CPU will be held then by non-RT task, and we have to update priority. I understand 1) and 2) to be, there has RT tasks on runqueue but they could not run at the moment. If throttled RQ == no RT tasks, please drop this patch directly. >> >> In another scenario that has little with {en, de}queue, as shown by >> requeue_task_rt(), the CPU priority will change if other RT tasks exist. >> > > The requeue_task_rt() does not change the priority of the CPU. It just > updates the task in its order of placement in the queue of other tasks > of the same priority. > You are right, updating CPU priority for requeue is unnecessary. thanks Hillf -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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