From afd41fff9c73ccc3757e94ad727d2a9ac4d7f6cb Mon Sep 17 00:00:00 2001 From: Nathan Huckleberry Date: Tue, 30 Aug 2022 18:44:44 +0000 Subject: dm verity: enable WQ_HIGHPRI on verify_wq WQ_HIGHPRI increases throughput and decreases disk latency when using dm-verity. This is important in Android for camera startup speed. The following tests were run by doing 60 seconds of random reads using a dm-verity device backed by two ramdisks. Without WQ_HIGHPRI lat (usec): min=13, max=3947, avg=69.53, stdev=50.55 READ: bw=51.1MiB/s (53.6MB/s), 51.1MiB/s-51.1MiB/s (53.6MB/s-53.6MB/s) With WQ_HIGHPRI: lat (usec): min=13, max=7854, avg=31.15, stdev=30.42 READ: bw=116MiB/s (121MB/s), 116MiB/s-116MiB/s (121MB/s-121MB/s) Further testing was done by measuring how long it takes to open a camera on an Android device. Without WQ_HIGHPRI Total verity work queue wait times (ms): 880.960, 789.517, 898.852 With WQ_HIGHPRI: Total verity work queue wait times (ms): 528.824, 439.191, 433.300 The average time to open the camera is reduced by 350ms (or 40-50%). Signed-off-by: Nathan Huckleberry Signed-off-by: Mike Snitzer --- drivers/md/dm-verity-target.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) (limited to 'drivers/md') diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c index 8a00cc42e498..ccf5b852fbf7 100644 --- a/drivers/md/dm-verity-target.c +++ b/drivers/md/dm-verity-target.c @@ -1401,14 +1401,16 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv) /* WQ_UNBOUND greatly improves performance when running on ramdisk */ wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND; - if (v->use_tasklet) { - /* - * Allow verify_wq to preempt softirq since verification in - * tasklet will fall-back to using it for error handling - * (or if the bufio cache doesn't have required hashes). - */ - wq_flags |= WQ_HIGHPRI; - } + /* + * Using WQ_HIGHPRI improves throughput and completion latency by + * reducing wait times when reading from a dm-verity device. + * + * Also as required for the "try_verify_in_tasklet" feature: WQ_HIGHPRI + * allows verify_wq to preempt softirq since verification in tasklet + * will fall-back to using it for error handling (or if the bufio cache + * doesn't have required hashes). + */ + wq_flags |= WQ_HIGHPRI; v->verify_wq = alloc_workqueue("kverityd", wq_flags, num_online_cpus()); if (!v->verify_wq) { ti->error = "Cannot allocate workqueue"; -- cgit v1.2.3