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

[Petr Vorel <pvorel@suse.cz>]

Hi Jens, all,

> On 7/19/24 11:43 AM, Petr Vorel wrote:
> > 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?

> No, because that got disabled before release for unrelated reasons. Why
> don't you just bisect it, since you have a simple test case?

Jens, thanks for info. Sure, I'll bisect next week and report.

The reason I reported before bisecting is because it wouldn't be the first time
the test was "artificial" and therefore reported problem was not fixed. If it's
a real problem I would expect it would be also caught by other people or even by
fstests.

Kind regards,
Petr