[PATCH] dm-verity: support block number limits for different ioprio classes

[LongPing Wei]

Calling verity_verify_io in bh for IO of all sizes is not suitable for
embedded devices. From our tests, it can improve the performance of 4K
synchronise random reads.
For example:
./fio --name=rand_read --ioengine=psync --rw=randread --bs=4K \
 --direct=1 --numjobs=8 --runtime=60 --time_based --group_reporting \
 --filename=/dev/block/mapper/xx-verity

But it will degrade the performance of 512K synchronise sequential reads
on our devices.
For example:
./fio --name=read --ioengine=psync --rw=read --bs=512K --direct=1 \
 --numjobs=8 --runtime=60 --time_based --group_reporting \
 --filename=/dev/block/mapper/xx-verity

A parameter array is introduced by this change. And users can modify the
default config by /sys/module/dm_verity/parameters/use_bh_blocks.

The default limits for NONE/RT/BE/IDLE is set to UINT_MAX to keep the
original behaviour.

Signed-off-by: LongPing Wei <weilongp...@oppo.com>
---
 drivers/md/dm-verity-target.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index e86c1431b108..1e0d0920d6a9 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -30,6 +30,7 @@
 #define DM_VERITY_ENV_VAR_NAME         "DM_VERITY_ERR_BLOCK_NR"
 
 #define DM_VERITY_DEFAULT_PREFETCH_SIZE        262144
+#define DM_VERITY_USE_BH_DEFAULT_BLOCKS        UINT_MAX
 
 #define DM_VERITY_MAX_CORRUPTED_ERRS   100
 
@@ -49,6 +50,15 @@ static unsigned int dm_verity_prefetch_cluster = 
DM_VERITY_DEFAULT_PREFETCH_SIZE
 
 module_param_named(prefetch_cluster, dm_verity_prefetch_cluster, uint, 0644);
 
+static unsigned int dm_verity_use_bh_blocks[4] = {
+       DM_VERITY_USE_BH_DEFAULT_BLOCKS,        // IOPRIO_CLASS_NONE
+       DM_VERITY_USE_BH_DEFAULT_BLOCKS,        // IOPRIO_CLASS_RT
+       DM_VERITY_USE_BH_DEFAULT_BLOCKS,        // IOPRIO_CLASS_BE
+       DM_VERITY_USE_BH_DEFAULT_BLOCKS         // IOPRIO_CLASS_IDLE
+};
+
+module_param_array_named(use_bh_blocks, dm_verity_use_bh_blocks, uint, NULL, 
0644);
+
 static DEFINE_STATIC_KEY_FALSE(use_bh_wq_enabled);
 
 /* Is at least one dm-verity instance using ahash_tfm instead of shash_tfm? */
@@ -652,6 +662,12 @@ static void verity_bh_work(struct work_struct *w)
        verity_finish_io(io, errno_to_blk_status(err));
 }
 
+static inline bool verity_use_bh(unsigned int n_blocks, unsigned short ioprio)
+{
+       return ioprio <= IOPRIO_CLASS_IDLE &&
+               n_blocks <= READ_ONCE(dm_verity_use_bh_blocks[ioprio]);
+}
+
 static void verity_end_io(struct bio *bio)
 {
        struct dm_verity_io *io = bio->bi_private;
@@ -664,7 +680,8 @@ static void verity_end_io(struct bio *bio)
                return;
        }
 
-       if (static_branch_unlikely(&use_bh_wq_enabled) && io->v->use_bh_wq) {
+       if (static_branch_unlikely(&use_bh_wq_enabled) && io->v->use_bh_wq &&
+               verity_use_bh(io->n_blocks, IOPRIO_PRIO_CLASS(bio->bi_ioprio))) 
{
                INIT_WORK(&io->bh_work, verity_bh_work);
                queue_work(system_bh_wq, &io->bh_work);
        } else {
-- 
2.34.1