On Fri, Jan 03, 2025 at 07:49:25AM +0100, Christoph Hellwig wrote: > On Thu, Jan 02, 2025 at 10:49:41AM +0100, Niklas Cassel wrote: > > > > from below information, it seems an 'ahci' to me. but since I have limited > > > > knowledge about storage driver, maybe I'm wrong. if you want more information, > > > > please let us know. thanks a lot! > > > > > > Yes, this looks like ahci. Thanks a lot! > > > > Did this ever get resolved? > > > > I haven't seen a patch that seems to address this. > > > > AHCI (ata_scsi_queuecmd()) only issues a single command, so if there is any > > reordering when issuing a batch of commands, my guess is that the problem > > also affects SCSI / the problem is in upper layers above AHCI, i.e. SCSI lib > > or block layer. > > I started looking into this before the holidays. blktrace shows perfectly > sequential writes without any reordering using ahci, directly on the > block device or using xfs and btrfs when using dd. I also started > looking into what the test does and got as far as checking out the > stress-ng source tree and looking at stress-aiol.c. AFAICS the default > submission does simple reads and writes using increasing offsets. > So if the test result isn't a fluke either the aio code does some > weird reordering or btrfs does. > > Oliver, did the test also show any interesting results on non-btrfs > setups? > One thing that came to mind. Some distros (e.g. Fedora and openSUSE) ship with an udev rule that sets the I/O scheduler to BFQ for single-queue HDDs. It could very well be the I/O scheduler that reorders. Oliver, which I/O scheduler are you using? $ cat /sys/block/sdb/queue/scheduler none mq-deadline kyber [bfq] Kind regards, Niklas
