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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 47abd24..2c1086a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2392,8 +2392,9 @@
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;
/*