doesn't work with bcache

[novaclark]

Ubuntu 20.04.4 LTS
Linux vcc-ldc-vs-10 5.4.0-113-generic #127-Ubuntu SMP Wed May 18 14:30:56 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Trying to run diskspd on a bcache device or mounted filesystem always results in the same error:

root@vcc-ldc-vs-10:~# df /mnt/tank/
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/bcache0 125020192760 871697380 124148495380 1% /mnt/tank

root@vcc-ldc-vs-10:~# diskspd -c8G -b512K -w50 -Sh -d60 -r4K /mnt/tank/testfile-delete.dat
ret from aio not equal to block size, it's -22
Error during warmup phase!
Job 0 failed, exiting

root@vcc-ldc-vs-10:~# umount /mnt/tank

root@vcc-ldc-vs-10:~# diskspd -b1M -w50 -Sh -d60 -r4K /dev/bcache0
ret from aio not equal to block size, it's -22
Error during thread initialization!
Job 0 failed, exiting

When writing to a filesystem, as in the former example, the test file is written before the error is displayed. When writing to the raw device the error is displayed after less than a second. The same commands work when run against the backing device only, or to the filesystem when only the backing device is mounted, but not to the bcache device or filesystem mounted thereon.

edited for better formatting and clarity.