Re: RSS in virtio spec

["Michael S. Tsirkin" <mst@redhat.com>]

Thanks!
This is worth clarifying in the spec, and maybe coming up with
a more formal definition than just a single example receiveq1 --> 0.


On Wed, Mar 01, 2023 at 10:56:31PM +0200, Yuri Benditovich wrote:
> Variant A
> Index N corresponds to receiveqÂ(N+1)Â
> 
> On Wed, Mar 1, 2023 at 7:29âPM Michael S. Tsirkin <mst@redhat.com> wrote:
> 
> 
> 
>     On Wed, Mar 01, 2023 at 07:17:19PM +0200, Yuri Benditovich wrote:
>     > HiÂMichael,
>     > I guess you mean https://github.com/oasis-tcs/virtio-spec/issues/135Â; Is
>     it
>     > correct?
> 
>     No.
> 
>     > I do not find words "queue index" in the respectiveÂdevice-types/net/
>     > description.tex
>     > It is stated in several places that "Index 0 corresponds to receiveq1"
>     > Sorry, but I do not exactly understand what is the issue? Can you please
>     > elaborate?Â
>     >
>     > Thanks,
>     > Yuri
>     >
>     > On Wed, Mar 1, 2023 at 12:28âPM Michael S. Tsirkin <mst@redhat.com>
>     wrote:
>     >
>     >Â Â ÂHi!
>     >Â Â ÂCould you pls comment on the issue of "queue index" in the
>     >Â Â Ârss indirection table? What is ment by that?
>     >
>     >Â Â ÂThanks!
>     >Â Â Â--
>     >Â Â ÂMST
>     >
> 
>     These two:
> 
> 
>     Field \field{unclassified_queue} contains the 0-based index of
>     the receive virtqueue to place unclassified packets in. Index 0 corresponds
>     to receiveq1.
> 
> 
>     ...
> 
>     Field \field{indirection_table} contains an array of 0-based indices of
>     receive virtqueus. Index 0 corresponds to receiveq1.
> 
> 
> 
>     BTW there's a typo virtqueus :)
> 
>     More importantly:
> 
>     What does "0-based indices of receive virtqueus" mean?
> 
>     Sure 0 is receiveq1. But how does one refer to receiveq3 ?
> 
>     A. we take the number after "q" and subtract 1. Thus receiveq2 -> 1.Â
>     receiveq3 -> 2
>     Â Âmax index is 0x7ffe higher indices are unused.
>     B. we take the index of the VQ. Thus receiveq2 -> 2, receiveq3 -> 4
>     Â Âmax index is 0xfffc and indices are even, odd indices would
>     Â Âcorrespond to transmitq and thus are unused for RSS.
> 
> 
> 
> 
>