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Jeff Moyer authored
Hi, Zhangqing Luo reported long boot times on a system with thousands of LUNs when scsi-mq was enabled. He narrowed the problem down to blk_mq_add_queue_tag_set, where every queue is frozen in order to set the BLK_MQ_F_TAG_SHARED flag. Each added device will freeze all queues added before it in sequence, which involves waiting for an RCU grace period for each one. We don't need to do this. After the second queue is added, only new queues need to be initialized with the shared tag. We can do that by percolating the flag up to the blk_mq_tag_set, and updating the newly added queue's hctxs if the flag is set. This problem was introduced by commit 0d2602ca (blk-mq: improve support for shared tags maps). Reported-and-tested-by:
Jason Luo <zhangqing.luo@oracle.com> Reviewed-by:
Ming Lei <ming.lei@canonical.com> Signed-off-by:
Jeff Moyer <jmoyer@redhat.com> Signed-off-by:
Jens Axboe <axboe@fb.com>
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