From 3ac0cc4508709d42ec9aa351086c7d38bfc0660c Mon Sep 17 00:00:00 2001 From: "shaohua.li@intel.com" Date: Fri, 6 May 2011 11:34:41 -0600 Subject: block: hold queue if flush is running for non-queueable flush drive In some drives, flush requests are non-queueable. When flush request is running, normal read/write requests can't run. If block layer dispatches such request, driver can't handle it and requeue it. Tejun suggested we can hold the queue when flush is running. This can avoid unnecessary requeue. Also this can improve performance. For example, we have request flush1, write1, flush 2. flush1 is dispatched, then queue is hold, write1 isn't inserted to queue. After flush1 is finished, flush2 will be dispatched. Since disk cache is already clean, flush2 will be finished very soon, so looks like flush2 is folded to flush1. In my test, the queue holding completely solves a regression introduced by commit 53d63e6b0dfb95882ec0219ba6bbd50cde423794: block: make the flush insertion use the tail of the dispatch list It's not a preempt type request, in fact we have to insert it behind requests that do specify INSERT_FRONT. which causes about 20% regression running a sysbench fileio workload. Stable: 2.6.39 only Cc: stable@kernel.org Signed-off-by: Shaohua Li Acked-by: Tejun Heo Signed-off-by: Jens Axboe --- block/blk.h | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) (limited to 'block/blk.h') diff --git a/block/blk.h b/block/blk.h index c9df8fc3c999..83e4bff36201 100644 --- a/block/blk.h +++ b/block/blk.h @@ -62,7 +62,26 @@ static inline struct request *__elv_next_request(struct request_queue *q) rq = list_entry_rq(q->queue_head.next); return rq; } - + /* + * Flush request is running and flush request isn't queueable + * in the drive, we can hold the queue till flush request is + * finished. Even we don't do this, driver can't dispatch next + * requests and will requeue them. And this can improve + * throughput too. For example, we have request flush1, write1, + * flush 2. flush1 is dispatched, then queue is hold, write1 + * isn't inserted to queue. After flush1 is finished, flush2 + * will be dispatched. Since disk cache is already clean, + * flush2 will be finished very soon, so looks like flush2 is + * folded to flush1. + * Since the queue is hold, a flag is set to indicate the queue + * should be restarted later. Please see flush_end_io() for + * details. + */ + if (q->flush_pending_idx != q->flush_running_idx && + !queue_flush_queueable(q)) { + q->flush_queue_delayed = 1; + return NULL; + } if (!q->elevator->ops->elevator_dispatch_fn(q, 0)) return NULL; } -- cgit v1.2.3