From da55f2cc78418dee88400aafbbaed19d7ac8188e Mon Sep 17 00:00:00 2001 From: Omar Sandoval Date: Wed, 22 Feb 2017 10:58:29 -0800 Subject: blk-mq: use sbq wait queues instead of restart for driver tags Commit 50e1dab86aa2 ("blk-mq-sched: fix starvation for multiple hardware queues and shared tags") fixed one starvation issue for shared tags. However, we can still get into a situation where we fail to allocate a tag because all tags are allocated but we don't have any pending requests on any hardware queue. One solution for this would be to restart all queues that share a tag map, but that really sucks. Ideally, we could just block and wait for a tag, but that isn't always possible from blk_mq_dispatch_rq_list(). However, we can still use the struct sbitmap_queue wait queues with a custom callback instead of blocking. This has a few benefits: 1. It avoids iterating over all hardware queues when completing an I/O, which the current restart code has to do. 2. It benefits from the existing rolling wakeup code. 3. It avoids punting to another thread just to have it block. Signed-off-by: Omar Sandoval Signed-off-by: Jens Axboe --- include/linux/blk-mq.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 8e4df3d6c8cd..001d30d727c5 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -33,6 +33,7 @@ struct blk_mq_hw_ctx { struct blk_mq_ctx **ctxs; unsigned int nr_ctx; + wait_queue_t dispatch_wait; atomic_t wait_index; struct blk_mq_tags *tags; @@ -160,6 +161,7 @@ enum { BLK_MQ_S_STOPPED = 0, BLK_MQ_S_TAG_ACTIVE = 1, BLK_MQ_S_SCHED_RESTART = 2, + BLK_MQ_S_TAG_WAITING = 3, BLK_MQ_MAX_DEPTH = 10240, -- cgit