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

Michael S. Tsirkin
2023-05-18T10:10:09Z

On Thu, May 18, 2023 at 08:47:22AM +0800, zhenwei pi wrote:
> On 5/17/23 18:39, Michael S. Tsirkin wrote:
> > 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 ...
> >
>
> Could you please take a look at this code?
> https://github.com/pizhenwei/linux/blob/virtio-of-github/drivers/virtio/virtio_fabrics.c#LL861C13-L861C23

what am I looking at here?

Looks like at least vof_handle_vq duplicates some code from vringh.
But besides that yes, that's the idea.

> >
> > > 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
> >
>
> --
> zhenwei pi