path: root/block
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authorJan Kara <>2016-01-12 16:24:17 +0100
committerJens Axboe <>2016-02-04 09:50:14 -0700
commita257ae3e482e1cbd5fc573efeef5a73bffe09757 (patch)
tree514bff67f2e6a1de70478038d410ff5895f08a45 /block
parent6c80731c75bd3289d35b89a21a4e317cbcb306e3 (diff)
cfq-iosched: Allow sync noidle workloads to preempt each other
The original idea with preemption of sync noidle queues (introduced in commit 718eee0579b8 "cfq-iosched: fairness for sync no-idle queues") was that we service all sync noidle queues together, we don't idle on any of the queues individually and we idle only if there is no sync noidle queue to be served. This intention also matches the original test: if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD && new_cfqq->service_tree == cfqq->service_tree) return true; However since at that time cfqq->service_tree was not set for idling queues, this test was unreliable and was replaced in commit e4a229196a7c "cfq-iosched: fix no-idle preemption logic" by: if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD && cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD && new_cfqq->service_tree->count == 1) return true; That was a reliable test but was actually doing something different - now we preempt sync noidle queue only if the new queue is the only one busy in the service tree. These days cfq queue is kept in service tree even if it is idling and thus the original check would be safe again. But since we actually check that cfq queues are in the same cgroup, of the same priority class and workload type (sync noidle), we know that new_cfqq is fine to preempt cfqq. So just remove the service tree check. Acked-by: Tejun Heo <> Signed-off-by: Jan Kara <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'block')
1 files changed, 0 insertions, 1 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 2544c219c00c..98569c2f373e 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3969,7 +3969,6 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
/* Allow preemption only if we are idling on sync-noidle tree */
if (cfqd->serving_wl_type == SYNC_NOIDLE_WORKLOAD &&
cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
- new_cfqq->service_tree->count == 2 &&
return true;