blkcg: make request_queue bypassing on allocation
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. The boot time overhead was pointed out by Vivek. Signed-off-by: NTejun Heo <tj@kernel.org> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: NJens Axboe <axboe@kernel.dk>
Showing
想要评论请 注册 或 登录