On 10/12/2014 02:41, Ming Lei wrote: > On Wed, Dec 10, 2014 at 1:45 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: >> >> >> On 08/12/2014 08:19, Ming Lei wrote: >>>>> >>>>> Alternatively, I'd accept a SCSI patch setting max_ws_blocks and friends >>>>> to 2GB - 1 block. >>> It should be better to not introduce the limit and split the writes >>> into size of 2GB - 1 block since there is only the limit for write zero. >> >> Why? That's exactly what the max_ws_blocks is for, and there's code in >> the guest already to do the split. We're talking about 2GB, not 1MB. > > The split in write same does not cover write zero, and that is the problem. > Otherwise write same just works fine. That said write same of QEMU SCSI > can work well without max write same sectors limit. > > If we introduce the limit of max write same sectors, this limit will be put > on both write zero and write non-zero path.
Yeah, but the 2GB limit happens also for the regular I/O path. The quirk is that it doesn't happen for non-zero WRITE SAME, not the other way round. > Also "MAXIMUM WRITE SAME LENGTH" is just introduced on sbc3r35 > in Jan, 2013, and some old host drivers may not support it, and not using > the limit should have better compatibility. Again, we're talking of 2GB and this is something that should never happen in practice. I'll write the patch myself. Paolo > Thanks, > Ming Lei > >
