diff options
| author | Omar Sandoval <osandov@fb.com> | 2017-02-22 10:58:29 -0800 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2017-02-23 11:55:46 -0700 |
| commit | da55f2cc78418dee88400aafbbaed19d7ac8188e (patch) | |
| tree | 59e8fea4c15519bfd0cfed355f59bf30d5d8e03d /include/linux/blk-mq.h | |
| parent | 2d19020b085eaf61d24377db27e8630cd9cff7ce (diff) | |
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 <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'include/linux/blk-mq.h')
| -rw-r--r-- | include/linux/blk-mq.h | 2 |
1 files changed, 2 insertions, 0 deletions
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, |