Re: [Qemu-stable] [Qemu-devel] [PATCH] block: fix big write

[Ming Lei]

On Wed, Dec 10, 2014 at 1:45 AM, Paolo Bonzini <address@hidden> 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.

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.

Thanks,
Ming Lei