On Wed, 26 Mar 2025, LongPing Wei wrote:
> 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_bytes.
>
> The default limits for NONE/RT/BE/IDLE is set to 4096.
>
> Call verity_verify_io directly when verity_end_io is in softirq.
>
> Signed-off-by: LongPing Wei <weilongp...@oppo.com>
Are you sure that 4096 bytes is the correct threshold?
I suggest that you run the benchmarks for 4k, 8k, 16k, 32k, 64k, 128k,
256k, 512k and set the default threshold to the largest value where bh
code performs better than non-bh code.
Mikulas
