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cfq-iosched: fix no-idle preemption logic

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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>
This commit is contained in:
Corrado Zoccolo 2009-11-26 10:02:58 +01:00 committed by Jens Axboe
parent e459dd08f4
commit e4a229196a
1 changed files with 3 additions and 2 deletions
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5
block/cfq-iosched.c
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@ -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;
/*