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. Cc: Ming Lei <ming.lei@xxxxxxxxxx> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Martijn Coenen <maco@xxxxxxxxxxx> Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx> --- drivers/block/loop.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index f8486d9b75a4..9fca3ab3988d 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -2333,7 +2333,8 @@ static int loop_add(int i) lo->tag_set.queue_depth = 128; lo->tag_set.numa_node = NUMA_NO_NODE; lo->tag_set.cmd_size = sizeof(struct loop_cmd); - lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_STACKING; + lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_STACKING | + BLK_MQ_F_NO_SCHED; lo->tag_set.driver_data = lo; err = blk_mq_alloc_tag_set(&lo->tag_set);
