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authorJens Axboe <axboe@fb.com>2017-01-26 22:40:07 +0300
committerJens Axboe <axboe@fb.com>2017-01-27 18:20:35 +0300
commitc13660a08c8b3bb49def4374bfd414aaaa564662 (patch)
treec7a61741aba75e320838865f176092c07af37f95 /block/blk-mq-sched.c
parent50e1dab86aa2c10cbca2f754aae9542169403141 (diff)
downloadlinux-c13660a08c8b3bb49def4374bfd414aaaa564662.tar.xz
blk-mq-sched: change ->dispatch_requests() to ->dispatch_request()
When we invoke dispatch_requests(), the scheduler empties everything into the passed in list. This isn't always a good thing, since it means that we remove items that we could have potentially merged with. Change the function to dispatch single requests at the time. If we do that, we can backoff exactly at the point where the device can't consume more IO, and leave the rest with the scheduler for better merging and future dispatch decision making. Signed-off-by: Jens Axboe <axboe@fb.com> Reviewed-by: Omar Sandoval <osandov@fb.com> Tested-by: Hannes Reinecke <hare@suse.com>
Diffstat (limited to 'block/blk-mq-sched.c')
-rw-r--r--block/blk-mq-sched.c23
1 files changed, 15 insertions, 8 deletions
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index fcc0e893d687..c27613de80c5 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -201,15 +201,22 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
* leave them there for as long as we can. Mark the hw queue as
* needing a restart in that case.
*/
- if (list_empty(&rq_list)) {
- if (e && e->type->ops.mq.dispatch_requests)
- e->type->ops.mq.dispatch_requests(hctx, &rq_list);
- else
- blk_mq_flush_busy_ctxs(hctx, &rq_list);
- } else
+ if (!list_empty(&rq_list)) {
blk_mq_sched_mark_restart(hctx);
-
- blk_mq_dispatch_rq_list(hctx, &rq_list);
+ blk_mq_dispatch_rq_list(hctx, &rq_list);
+ } else if (!e || !e->type->ops.mq.dispatch_request) {
+ blk_mq_flush_busy_ctxs(hctx, &rq_list);
+ blk_mq_dispatch_rq_list(hctx, &rq_list);
+ } else {
+ do {
+ struct request *rq;
+
+ rq = e->type->ops.mq.dispatch_request(hctx);
+ if (!rq)
+ break;
+ list_add(&rq->queuelist, &rq_list);
+ } while (blk_mq_dispatch_rq_list(hctx, &rq_list));
+ }
}
void blk_mq_sched_move_to_dispatch(struct blk_mq_hw_ctx *hctx,