On Fri, Aug 07, 2020 at 05:05:59PM +0800, Chao Leng wrote: > nvme_stop_queues quiesce queues for all name spaces, now quiesce one by > one, if there is lots of name spaces, sync wait long time(more than 10s). > Multipath can not fail over to retry quickly, cause io pause long time. > This is not expected. > To reduce quiesce time, we introduce async mechanism for sync SRCUs > and quiesce queue. > Frankly speaking, I prefer to replace SRCU with percpu_refcount: - percpu_refcount has much less memory footprint than SRCU, so we can simply move percpu_refcount into request_queue, instead of adding more bytes into each hctx by this patch - percpu_ref_get()/percpu_ref_put() isn't slower than srcu_read_lock()/srcu_read_unlock(). - with percpu_refcount, we can remove 'srcu_idx' from hctx_lock/hctx_unlock() Thanks, Ming
