Commit e4a22919 authored Nov 26, 2009 by Corrado Zoccolo Committed by Jens Axboe Nov 26, 2009

cfq-iosched: fix no-idle preemption logic



An incoming no-idle queue should preempt the active no-idle queue
 only if the active queue is idling due to service tree empty.
 Previous code was buggy in two ways:
 * it relied on service_tree field to be set on the active queue, while
   it is not set when the code is idling for a new request
 * it didn't check for the service tree empty condition, so could lead to
   LIFO behaviour if multiple queues with depth > 1 were preempting each
   other on an non-NCQ device.

Reported-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

parent e459dd08

block/cfq-iosched.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -2392,8 +2392,9 @@ cfq_should_preempt(struct cfq_data cfqd, struct cfq_queue new_cfqq,
		if (cfq_class_idle(cfqq))
		return true;

		if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD
		&& new_cfqq->service_tree == cfqq->service_tree)
		if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
		cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
		new_cfqq->service_tree->count == 1)
		return true;

		/*

Admin message