From e4a229196a7c676514c78f6783f8994f64bf681c Mon Sep 17 00:00:00 2001 From: Corrado Zoccolo Date: Thu, 26 Nov 2009 10:02:58 +0100 Subject: [PATCH] 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 Signed-off-by: Corrado Zoccolo Acked-by: Vivek Goyal Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) 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 @@ 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; /* -- 2.7.4