cfq-iosched: schedule dispatch for noidle queue (d2d59e18) · Commits · 戴 / test

A queue is idle at cfq_dispatch_requests(), but it gets noidle later. Unless other task explictly does unplug or all requests are drained, we will not deliever requests to the disk even cfq_arm_slice_timer doesn't make the queue idle. For example, cfq_should_idle() returns true because of service_tree->count == 1, and then other queues are added. Note, I didn't see obvious performance impacts so far with the patch, but just thought this could be a problem. Signed-off-by:

Shaohua Li <shaohua.li@intel.com> Signed-off-by:

Jens Axboe <jaxboe@fusionio.com>

block/cfq-iosched.c

+22 −1

Original line number	Diff line number	Diff line
		@@ -3255,6 +3255,10 @@ cfq_should_preempt(struct cfq_data cfqd, struct cfq_queue new_cfqq,
		if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
		return true;

		/* An idle queue should not be idle now for some reason */
		if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq))
		return true;

		if (!cfqd->active_cic \|\| !cfq_cfqq_wait_request(cfqq))
		return false;

		@@ -3508,8 +3512,25 @@ static void cfq_completed_request(struct request_queue q, struct request rq)
		}
		}

		if (!cfqd->rq_in_driver)
		if (!cfqd->rq_in_driver) {
		cfq_schedule_dispatch(cfqd);
		return;
		}
		/*
		* A queue is idle at cfq_dispatch_requests(), but it gets noidle
		* later. We schedule a dispatch if the queue has no requests,
		* otherwise the disk is actually in idle till all requests
		* are finished even cfq_arm_slice_timer doesn't make the queue idle
		* */
		cfqq = cfqd->active_queue;
		if (!cfqq)
		return;

		if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq) &&
		(!cfqd->cfq_group_idle \|\| cfqq->cfqg->nr_cfqq > 1)) {
		cfq_del_timer(cfqd, cfqq);
		cfq_schedule_dispatch(cfqd);
		}
		}

		/*

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