In some drives, flush requests are non-queueable. This means when a flush request
is running, normal read/write requests are not. In such drive, when running flush
requests finish, we can make pending flush requests finish. Since normal write
requests are not running, pending flush requests also flush required drive cache
out. This reduces some flush requests running and improve performance.
This patch allows block core utilizes the optimization. Next patch will enable it
for SATA.
Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
---
block/blk-flush.c | 15 +++++++++++++--
include/linux/blkdev.h | 11 +++++++++++
2 files changed, 24 insertions(+), 2 deletions(-)
Index: linux/block/blk-flush.c
===================================================================
--- linux.orig/block/blk-flush.c 2011-04-19 09:21:47.000000000 +0800
+++ linux/block/blk-flush.c 2011-04-19 16:38:22.000000000 +0800
@@ -193,18 +193,29 @@ static bool blk_flush_complete_seq(struc
static void flush_end_io(struct request *flush_rq, int error)
{
struct request_queue *q = flush_rq->q;
- struct list_head *running = &q->flush_queue[q->flush_running_idx];
+ LIST_HEAD(proceed_list);
bool queued = false;
struct request *rq, *n;
BUG_ON(q->flush_pending_idx == q->flush_running_idx);
+ list_splice_init(&q->flush_queue[q->flush_running_idx], &proceed_list);
+ /*
+ * If queue doesn't support queueable flush request, we can push the
+ * pending requests to the next stage too. For such queue, there are no
+ * normal requests running when flush request is running, so this still
+ * guarantees the correctness.
+ */
+ if (!blk_queue_flush_queueable(q))
+ list_splice_tail_init(&q->flush_queue[q->flush_pending_idx],
+ &proceed_list);
+
/* account completion of the flush request */
q->flush_running_idx ^= 1;
elv_completed_request(q, flush_rq);
/* and push the waiting requests to the next stage */
- list_for_each_entry_safe(rq, n, running, flush.list) {
+ list_for_each_entry_safe(rq, n, &proceed_list, flush.list) {
unsigned int seq = blk_flush_cur_seq(rq);
BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
Index: linux/include/linux/blkdev.h
===================================================================
--- linux.orig/include/linux/blkdev.h 2011-04-19 09:15:15.000000000 +0800
+++ linux/include/linux/blkdev.h 2011-04-19 10:04:46.000000000 +0800
@@ -366,6 +366,7 @@ struct request_queue
* for flush operations
*/
unsigned int flush_flags;
+ unsigned int flush_not_queueable:1;
unsigned int flush_pending_idx:1;
unsigned int flush_running_idx:1;
unsigned long flush_pending_since;
@@ -552,6 +553,16 @@ static inline void blk_clear_queue_full(
queue_flag_clear(QUEUE_FLAG_ASYNCFULL, q);
}
+static inline void blk_set_queue_flush_queueable(struct request_queue *q,
+ bool queueable)
+{
+ q->flush_not_queueable = !queueable;
+}
+
+static inline bool blk_queue_flush_queueable(struct request_queue *q)
+{
+ return !q->flush_not_queueable;
+}
/*
* mergeable request must not have _NOMERGE or _BARRIER bit set, nor may
--
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