path: root/block
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authorJan Kara <>2015-11-12 14:25:52 +0100
committerJens Axboe <>2015-11-16 15:23:51 -0700
commit1b2ff19e6a957b1ef0f365ad331b608af80e932e (patch)
tree095d2ee5738318c4065236a14de0c03e9105d022 /block
parentb2b7e00148a203e9934bbd17aebffae3f447ade7 (diff)
blk-flush: Queue through IO scheduler when flush not required
Currently blk_insert_flush() just adds flush request to q->queue_head when flush is not required. That completely bypasses IO scheduler so e.g. CFQ can be idling waiting for new request to arrive and will idle through the whole window unnecessarily. Luckily this only happens in rare cases as usually checks in generic_make_request_checks() clear FLUSH and FUA flags early if they are not needed. When no flushing is actually required, we can easily fix the problem by properly queueing the request through the IO scheduler. Ideally IO scheduler should be also made aware of requests queued via blk_flush_queue_rq(). However inserting flush request through IO scheduler can have unwanted side-effects since due to flush batching delaying the flush request in IO scheduler will delay all flush requests possibly coming from other processes. So we keep adding the request directly to q->queue_head. Signed-off-by: Jan Kara <> Reviewed-by: Jeff Moyer <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'block')
1 files changed, 1 insertions, 1 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 9c423e53324a..c81d56ec308f 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -422,7 +422,7 @@ void blk_insert_flush(struct request *rq)
if (q->mq_ops) {
blk_mq_insert_request(rq, false, false, true);
} else
- list_add_tail(&rq->queuelist, &q->queue_head);
+ q->elevator->type->ops.elevator_add_req_fn(q, rq);