On 2020/05/14 9:22, Martin K. Petersen wrote: > > Damien, > >> Any idea why the io_opt limit is not set to the physical block size >> when the drive does not report an optimal transfer length ? Would it >> be bad to set that value instead of leaving it to 0 ? > > The original intent was that io_opt was a weak heuristic for something > being a RAID device. Regular disk drives didn't report it. These days > that distinction probably isn't relevant. > > However, before we entertain departing from the historic io_opt > behavior, I am a bit puzzled by the fact that you have a device that > reports io_opt as 512 bytes. What kind of device performs best when each > I/O is limited to a single logical block? > Indeed. It is an NVMe M.2 consumer grade SSD. Nothing fancy. If you look at nvme/host/core.c nvme_update_disk_info(), you will see that io_opt is set to the block size... This is probably abusing this limit. So I guess the most elegant fix may be to have nvme stop doing that ? -- Damien Le Moal Western Digital Research -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
