From: Jens Axboe <axboe@fb.com>
Date: Wed, 29 Oct 2014 17:18:26 +0000 (-0600)
Subject: blk-mq: add BLK_MQ_F_DEFER_ISSUE support flag
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=e167dfb53cb85fde7b15f644e9dbef7ba31896b6;p=openwrt%2Fstaging%2Fblogic.git

blk-mq: add BLK_MQ_F_DEFER_ISSUE support flag

Drivers can now tell blk-mq if they take advantage of the deferred
issue through 'last' or not. If they do, don't do queue-direct
for sync IO. This is a preparation patch for the nvme conversion.

Signed-off-by: Jens Axboe <axboe@fb.com>
---

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7e5303820452..b355b5957cd7 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1172,7 +1172,12 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		goto run_queue;
 	}
 
-	if (is_sync) {
+	/*
+	 * If the driver supports defer issued based on 'last', then
+	 * queue it up like normal since we can potentially save some
+	 * CPU this way.
+	 */
+	if (is_sync && !(data.hctx->flags & BLK_MQ_F_DEFER_ISSUE)) {
 		struct blk_mq_queue_data bd = {
 			.rq = rq,
 			.list = NULL,
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index be01d7a687d4..c3b64ec5321e 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -146,6 +146,7 @@ enum {
 	BLK_MQ_F_TAG_SHARED	= 1 << 1,
 	BLK_MQ_F_SG_MERGE	= 1 << 2,
 	BLK_MQ_F_SYSFS_UP	= 1 << 3,
+	BLK_MQ_F_DEFER_ISSUE	= 1 << 4,
 
 	BLK_MQ_S_STOPPED	= 0,
 	BLK_MQ_S_TAG_ACTIVE	= 1,