Re: [virtio] [PATCH] virtqueue: flexible layout, size, alignment

[Rusty Russell <rusty@au1.ibm.com>]

"Michael S. Tsirkin" <mst@redhat.com> writes:
> On Fri, Sep 13, 2013 at 10:40:40AM +0930, Rusty Russell wrote:
>> "Michael S. Tsirkin" <mst@redhat.com> writes:
>> > ++------------+---------------------------------+
>> > +| Virtqueue Part    | Alignment | Size         |
>> > ++------------+---------------------------------+
>> > ++------------+---------------------------------+
>> > +| Descriptor Table  | 16        | 16 * qsz     |
>> 
>> Alignment 16: isn't that overkill?
>
> Why overkill? 16 bytes is exactly a single descriptor size,
> aligning descriptor buffer to descriptor size seems sensible,
> it simplifies translation: this we never cross a page boundary
> in the middle of descriptor.

Otherwise I was thinking 8 byte alignment (the largest element).  But
the page boundary point makes great sense.

Cheers,
Rusty.