Re: [virtio-dev] packed ring layout proposal - todo list

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

On Tue, Feb 28, 2017 at 12:29:43PM +0800, Yuanhan Liu wrote:
> Hi Michael,
> 
> Again, as usual, sorry for being late :/
> 
> On Wed, Feb 22, 2017 at 06:27:11AM +0200, Michael S. Tsirkin wrote:
> > Stage 2: prototype guest/host drivers
> > 
> > At this stage we need real guest and host drivers
> > to be able to test real life performance.
> > I suggest dpdk drivers + munimal hack in qemu to
> > pass features around.
> > 
> 
> I have already done that in last Nov. I made a very rough (yet hacky)
> version (only with Tx path) in one day while companying my wife in
> hospital.

Any performance data?

> If someone are interested in, I could share the code soon. I could
> even cleanup the code a bit if necessary.

Especially if you don't have time to benchmark, I think sharing it
might help.

> > Tasks:
> > 
> > - implement vhost-user support in dpdk
> > - implement virtio support in dpdk
> > - implement minimal stub in qemu
> 
> I didn't hack the QEMU, instead, I hacked the DPDK virtio-user, yet
> another virtio-net emulation. It's simpler and quicker for me.

Sure, I merely meant a stub for negotiating new feature bits
between host and guest. But I guess an environment set
the same way in host and guest would serve too.

> And here is my plan on virtio 1.1:
> 
> - Look deeper inside the virtio net performance issues (WIP)
> 
>   It's basically a job about digging the DPDK vhost/virtio code
>   deeper, something like how exactly the cache acts while Tx/Rx
>   pkts, what can be optimized by implementation, and what could
>   be improved with the help of spec extension.
> 
>   Please note that I often got interrupted on this task: it didn't
>   go smooth as I would have expected.
> 
> 
> - Try to accelerate vhost/virtio with vector instructions.

That's interesting. What kind of optimizations would you say
do vector instructions enable, and why?


>   Something I will look into when above item is done. Currently,
>   I thought of two items may help the vector implementation:
> 
>   * what kind of vring and desc layout could make the vector
>     implementation easier.
> 
>   * what kind of hint we need from virtio spec for (dynamically)
>     enabling the vector path.
> 
>   Besides that, I don't have too much clue yet.
> 
> 	--yliu