On Mon, Aug 02, 2021 at 10:23:56PM -0700, Bart Van Assche wrote: > On 8/2/21 6:54 PM, Ming Lei wrote: > > On Mon, Aug 02, 2021 at 05:01:59PM -0700, Bart Van Assche wrote: > >> Loop devices have a single hardware queue. Hence, the block layer function > >> elevator_get_default() selects the mq-deadline scheduler for loop devices. > >> Using the mq-deadline scheduler or any other I/O scheduler for loop devices > >> incurs unnecessary overhead. Make the loop driver pass the flag > >> BLK_MQ_F_NOSCHED to the block layer core such that no I/O scheduler can be > >> associated with block devices. This approach has an advantage compared to > >> letting udevd change the loop I/O scheduler to none, namely that > >> synchronize_rcu() does not get called. > >> > >> It is intentional that the flag BLK_MQ_F_SHOULD_MERGE is preserved. > >> > >> This patch reduces the Android boot time on my test setup with 0.5 seconds. > > > > Can you investigate why none reduces Android boot time? Or reproduce & > > understand it by a fio simulation on your setting? > > Hi Ming, > > The software process called apexd creates multiple loop devices while > the device is booting. Using BLK_MQ_F_NO_SCHED is faster than letting > apexd change the I/O scheduler from mq-deadline into 'none' since the > latter involves calling synchronize_rcu() once per loop device. OK, but why does apexd switch to none during booting? Does none perform better than deadline during booting in the Android setting? Thanks, Ming
