Re: Re: [PATCH v2 1/2] virtio: abstract virtqueue related methods

Michael S. Tsirkin
2023-05-17T10:40:42Z

On Wed, May 17, 2023 at 04:35:55PM +0800, zhenwei pi wrote:
>
>
> On 5/17/23 15:46, Christoph Hellwig wrote:
> > On Wed, May 17, 2023 at 03:43:03PM +0800, zhenwei pi wrote:
> > > I have a plan to introduce 'Virtio Over Fabrics'(TCP&RDMA) as Virtio
> > > transport, as mentioned in cover letter of this series:
> > > 3 weeks ago, I posted a proposal 'Virtio Over Fabrics':
> > > https://lists.oasis-open.org/archives/virtio-comment/202304/msg00442.html
> >
> > Just don't do it. Please define your own protocols over RDMA or TCP
> > for exactly the operations you need (for many they will already exist)
> > instead of piggyg backing on virtio and making everyone else pay the
> > price.
> >
>
> Hi
>
> 1, `virtqueue_add_inbuf` in current version:
> static inline int virtqueue_add_inbuf(struct virtqueue *vq,
> struct scatterlist *sg,
> unsigned int num,
> void *data,
> gfp_t gfp)
> {
> if (likely(!vq->abstract))
> return vring_virtqueue_add_sgs(vq, &sg, num, 0, 1, data,
> NULL, gfp);
>
> return vq->add_sgs(vq, &sg, num, 0, 1, data, NULL, gfp);
> }
>
> And disassemble 'virtinput_queue_evtbuf':
> static void virtinput_queue_evtbuf(struct virtio_input *vi,
> struct virtio_input_event *evtbuf)
> {
> struct scatterlist sg[1];
>
> sg_init_one(sg, evtbuf, sizeof(*evtbuf));
> virtqueue_add_inbuf(vi->evt, sg, 1, evtbuf, GFP_ATOMIC);
> }
>
> I notice that two instructions are newly added for vring like:
> 24d: 80 78 35 00 cmpb $0x0,0x35(%rax)
> 251: 75 3f jne 292
>
> Is it an expensive price...

Can we somehow only override the kick method?
Then take the ring and send it over ...

> 2, Storage/FS specific remote protocol is quite popular, otherwise I'm not
> familiar with other device protocols. For example, I need a remote crypto
> device to accelerate HTTPS ... With Virtio Over Fabrics, I have a chance to
> attach a virtio-crypto device to do this work.
>
> --
> zhenwei pi