[RFC] Slow down of LTP tests aiodio_sparse.c and dio_sparse.c in kernel 6.6

[Petr Vorel <pvorel@suse.cz>]

Hi all,

LTP AIO DIO tests aiodio_sparse.c [1] and dio_sparse.c [2] (using [3]) slowed
down on kernel 6.6 on Btrfs and XFS, when run with default parameters. These
tests create 100 MB sparse file and write zeros (using libaio or O_DIRECT) while
16 other processes reads the buffer and check only zero is there.

Runtime of this particular setup (i.e. 100 MB file) on Btrfs and XFS on the
same system slowed down 9x (6.5: ~1 min 6.6: ~9 min). Ext4 is not affected.
(Non default parameter creates much smaller file, thus the change is not that
obvious).

Because the slowdown has been here for few kernel releases I suppose nobody
complained and the test is somehow artificial (nobody uses this in a real world).
But still it'd be good to double check the problem. I can bisect a particular
commit.

Because 2 filesystems affected, could be "Improve asynchronous iomap DIO
performance" [4] block layer change somehow related?

Kind regards,
Petr

[1] https://github.com/linux-test-project/ltp/tree/master/testcases/kernel/io/ltp-aiodio/aiodio_sparse.c
[2] https://github.com/linux-test-project/ltp/tree/master/testcases/kernel/io/ltp-aiodio/dio_sparse.c
[3] https://github.com/linux-test-project/ltp/tree/master/testcases/kernel/io/ltp-aiodio/common.h
[4] https://kernelnewbies.org/Linux_6.6#Block_layer