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

[Jens Axboe <axboe@kernel.dk>]

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 Axboe