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. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
