Re: [PATCH 3/4] blk-mq: use hw tag for scheduling if hw tag space is big enough

On Wed, May 03, 2017 at 09:29:36AM -0700, Omar Sandoval wrote:

On Fri, Apr 28, 2017 at 11:15:38PM +0800, Ming Lei wrote:

quoted

When tag space of one device is big enough, we use hw tag
directly for I/O scheduling.

Now the decision is made if hw queue depth is not less than
q->nr_requests and the tag set isn't shared.

Signed-off-by: Ming Lei <redacted>
---
 block/blk-mq-sched.c |  8 ++++++++
 block/blk-mq-sched.h | 15 +++++++++++++++
 block/blk-mq.c       | 18 +++++++++++++++++-
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 45a675f07b8b..4681e27c127e 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c

@@ -507,6 +507,7 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 	struct elevator_queue *eq;
 	unsigned int i;
 	int ret;
+	bool auto_hw_tag;
 
 	if (!e) {
 		q->elevator = NULL;

@@ -519,7 +520,14 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 	 */
 	q->nr_requests = 2 * BLKDEV_MAX_RQ;
 
+	auto_hw_tag = blk_mq_sched_may_use_hw_tag(q);
+
 	queue_for_each_hw_ctx(q, hctx, i) {
+		if (auto_hw_tag)
+			hctx->flags |= BLK_MQ_F_SCHED_USE_HW_TAG;
+		else
+			hctx->flags &= ~BLK_MQ_F_SCHED_USE_HW_TAG;
+
 		ret = blk_mq_sched_alloc_tags(q, hctx, i);
 		if (ret)
 			goto err;

I think you should also clear the BLK_MQ_F_SCHED_USE_HW_TAG flag in
blk_mq_exit_sched()?

Looks not necessary since the flag is always evaluated in
blk_mq_init_sched().

Thanks,
Ming