On Tue, Oct 28, 2014 at 04:22:55PM -0400, Tejun Heo wrote: > On Tue, Oct 28, 2014 at 09:20:55PM +0100, Christian Borntraeger wrote: > > I have not verified this, but I guess what happens is: > > hotplug > > -> notify > > -> blk_mq_queue_reinit_notify > > -> blk_mq_queue_reinit > > -> blk_mq_freeze_queue > > -> percpu_ref_kill > > -> percpu_ref_kill_and_confirm > > -> __percpu_ref_switch_to_atomic > > -> call_rcu_sched > > But call_rcu_sched() wouldn't show up as latency. It's an async call > unlike synchronize_*().
I got confused, so perpcu_ref does wait for the async grace period making it synchronous. I see what you mean. This isn't during init but freezing itself being slow. Hmmmm... so are you seeing multiple queues doing that back-to-back? If so, the right thing to do would be making the freezing take place in parallel. I'll look into it. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
