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authorshaohua.li@intel.com <shaohua.li@intel.com>2011-05-06 21:34:41 +0400
committerJens Axboe <jaxboe@fusionio.com>2011-05-06 21:36:25 +0400
commit3ac0cc4508709d42ec9aa351086c7d38bfc0660c (patch)
tree933d5ab6ff9b0763f36e614962abb5bdcc4a348a
parentf3876930952390a31c3a7fd68dd621464a36eb80 (diff)
downloadlinux-3ac0cc4508709d42ec9aa351086c7d38bfc0660c.tar.xz
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 <shaohua.li@intel.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
-rw-r--r--block/blk-flush.c16
-rw-r--r--block/blk.h21
-rw-r--r--include/linux/blkdev.h1
3 files changed, 32 insertions, 6 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 6c9b5e189e62..bb21e4c36f70 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -212,13 +212,19 @@ static void flush_end_io(struct request *flush_rq, int error)
}
/*
- * Moving a request silently to empty queue_head may stall the
- * queue. Kick the queue in those cases. This function is called
- * from request completion path and calling directly into
- * request_fn may confuse the driver. Always use kblockd.
+ * Kick the queue to avoid stall for two cases:
+ * 1. Moving a request silently to empty queue_head may stall the
+ * queue.
+ * 2. When flush request is running in non-queueable queue, the
+ * queue is hold. Restart the queue after flush request is finished
+ * to avoid stall.
+ * This function is called from request completion path and calling
+ * directly into request_fn may confuse the driver. Always use
+ * kblockd.
*/
- if (queued)
+ if (queued || q->flush_queue_delayed)
blk_run_queue_async(q);
+ q->flush_queue_delayed = 0;
}
/**
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;
}
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8bd2a271b2d8..9f921bf4bf8c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -365,6 +365,7 @@ struct request_queue
*/
unsigned int flush_flags;
unsigned int flush_not_queueable:1;
+ unsigned int flush_queue_delayed:1;
unsigned int flush_pending_idx:1;
unsigned int flush_running_idx:1;
unsigned long flush_pending_since;