On Tue, Jul 28, 2020 at 09:49:38PM +0800, Ming Lei wrote: > In case of BLK_MQ_F_BLOCKING, blk-mq uses SRCU to mark read critical > section during dispatching request, then request queue quiesce is based on > SRCU. What we want to get is low cost added in fast path. > > However, from srcu_read_lock/srcu_read_unlock implementation, not see > it is quicker than percpu refcount, so use percpu_ref to implement > queue quiesce. This usage is cleaner and simpler & enough for implementing > queue quiesce. The main requirement is to make sure all read sections to observe > QUEUE_FLAG_QUIESCED once blk_mq_quiesce_queue() returns. > > Also it becomes much easier to add interface of async queue quiesce. BTW, no obvious IOPS difference is observed with this patch applied when running io on null_blk(blocking, submit_queues=32) in one dual-socket, 32cores system. Thanks, Ming
