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

[Jan Kara <jack@suse.cz>]

Hi!

On Fri 19-07-24 19:43:25, Petr Vorel wrote:
> 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.

So the performance of this test is irrelevant because combining buffered
reads with direct IO writes was always in "better don't do it" territory.
Definitely not if you care about perfomance.

> 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).

But still it's kind of curious what caused the 9x slow down. So I'd be
curious to know the result of the bisection :). Thanks for report!

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR