On Fri, Apr 13, 2012 at 04:32:05PM -0400, Vivek Goyal wrote: > On Fri, Apr 13, 2012 at 01:11:31PM -0700, Tejun Heo wrote: > > With the previous change to guarantee bypass visiblity for RCU read > > lock regions, entering bypass mode involves non-trivial overhead and > > future changes are scheduled to make use of bypass mode during init > > path. Combined it may end up adding noticeable delay during boot. > > > > This patch makes request_queue start its life in bypass mode, which is > > ended on queue init completion at the end of > > blk_init_allocated_queue(), and updates blk_queue_bypass_start() such > > that draining and RCU synchronization are performed only when the > > queue actually enters bypass mode. > > > > This avoids unnecessarily switching in and out of bypass mode during > > init avoiding the overhead and any nasty surprises which may step from > > leaving bypass mode on half-initialized queues. > > Tejun, I am not sure that this will fix the problem completely. I think > we will still face the overhead of synchronize_rcu() in > blkcg_deactivate_policy() as it will be called from cfq_exit_queue() for > initialized queues. > > In the past I had I had used synchronize_rcu() in cfq_exit_queue() and > noticed the overhead. Looks like driver was creating fully initialized > queues and tearing these apart soon. blk_cleanup_queue() doesn't use blk_queue_bypass_start() to enter bypass mode. Thanks. -- tejun _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
