From 86ff7c2a80cd357f6156a53b354f6a0b357dc0c9 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Tue, 30 Jan 2018 22:04:57 -0500 Subject: blk-mq: introduce BLK_STS_DEV_RESOURCE This status is returned from driver to block layer if device related resource is unavailable, but driver can guarantee that IO dispatch will be triggered in future when the resource is available. Convert some drivers to return BLK_STS_DEV_RESOURCE. Also, if driver returns BLK_STS_RESOURCE and SCHED_RESTART is set, rerun queue after a delay (BLK_MQ_DELAY_QUEUE) to avoid IO stalls. BLK_MQ_DELAY_QUEUE is 3 ms because both scsi-mq and nvmefc are using that magic value. If a driver can make sure there is in-flight IO, it is safe to return BLK_STS_DEV_RESOURCE because: 1) If all in-flight IOs complete before examining SCHED_RESTART in blk_mq_dispatch_rq_list(), SCHED_RESTART must be cleared, so queue is run immediately in this case by blk_mq_dispatch_rq_list(); 2) if there is any in-flight IO after/when examining SCHED_RESTART in blk_mq_dispatch_rq_list(): - if SCHED_RESTART isn't set, queue is run immediately as handled in 1) - otherwise, this request will be dispatched after any in-flight IO is completed via blk_mq_sched_restart() 3) if SCHED_RESTART is set concurently in context because of BLK_STS_RESOURCE, blk_mq_delay_run_hw_queue() will cover the above two cases and make sure IO hang can be avoided. One invariant is that queue will be rerun if SCHED_RESTART is set. Suggested-by: Jens Axboe Tested-by: Laurence Oberman Signed-off-by: Ming Lei Signed-off-by: Mike Snitzer Signed-off-by: Jens Axboe --- drivers/md/dm-rq.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'drivers/md/dm-rq.c') diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c index b7d175e94a02..348a0cb6963a 100644 --- a/drivers/md/dm-rq.c +++ b/drivers/md/dm-rq.c @@ -404,7 +404,7 @@ static blk_status_t dm_dispatch_clone_request(struct request *clone, struct requ clone->start_time = jiffies; r = blk_insert_cloned_request(clone->q, clone); - if (r != BLK_STS_OK && r != BLK_STS_RESOURCE) + if (r != BLK_STS_OK && r != BLK_STS_RESOURCE && r != BLK_STS_DEV_RESOURCE) /* must complete clone in terms of original request */ dm_complete_request(rq, r); return r; @@ -496,7 +496,7 @@ check_again: trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)), blk_rq_pos(rq)); ret = dm_dispatch_clone_request(clone, rq); - if (ret == BLK_STS_RESOURCE) { + if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) { blk_rq_unprep_clone(clone); tio->ti->type->release_clone_rq(clone); tio->clone = NULL; @@ -769,7 +769,6 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx, /* Undo dm_start_request() before requeuing */ rq_end_stats(md, rq); rq_completed(md, rq_data_dir(rq), false); - blk_mq_delay_run_hw_queue(hctx, 100/*ms*/); return BLK_STS_RESOURCE; } -- cgit v1.2.3-59-g8ed1b