On 22/03/2018 08:38, Fam Zheng wrote: > Some backends report big max_io_sectors. Making min_io_size the same > value in this case will make it impossible for guest to align memory, > therefore the disk may not be usable at all. > > Change the default behavior (when min_io_size and opt_io_size are not > specified in the command line), do not assume max_io_sectors is a good > value for opt_io_size and min_io_size, use 512 instead. > > Reported-by: David Gibson <dgib...@redhat.com> > Signed-off-by: Fam Zheng <f...@redhat.com> > --- > hw/scsi/scsi-disk.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c > index 5b7a48f5a5..76e3c9eaa4 100644 > --- a/hw/scsi/scsi-disk.c > +++ b/hw/scsi/scsi-disk.c > @@ -714,10 +714,8 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, > uint8_t *outbuf) > > /* min_io_size and opt_io_size can't be greater than > * max_io_sectors */ > - min_io_size = > - MIN_NON_ZERO(min_io_size, max_io_sectors); > - opt_io_size = > - MIN_NON_ZERO(opt_io_size, max_io_sectors); > + min_io_size = MIN(min_io_size ? : 512, max_io_sectors); > + opt_io_size = MIN(opt_io_size ? : 512, max_io_sectors);
There are a few easily fixed issues with your chosen defaults, though the problem obviously makes sense: 1) the values are in sectors - since you chose 512, it's not clear if you meant it to be 512 bytes or 512 sectors. :) 512 sectors (256 KiB or 2 MiB depending on logical block size) is still too much for the min_io_size. The min_io_size default (if it is 0) is the physical block size, so I think we should make the min_io_size either 0 or the physical block size. 2) For the opt_io_size, 256 KiB on the other hand is probably too little. On my laptop (NVMe disk) a transfer size of 8 MiB is twice as fast compared to a transfer size of 256 KiB, and 16 MiB or 32 MiB is a little faster too. I would either leave zero as the default, or pick something around 16-32 MiB. Thanks, Paolo > } > /* required VPD size with unmap support */ > buflen = 0x40; >
