On Wed, Jul 29, 2020 at 08:42:31AM -0700, Sagi Grimberg 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, can you test for non-blocking on the same setup? OK, I can do that, but this patch supposes to not affect non-blocking, care to share your motivation for testing non-blocking? Thanks, Ming
