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

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Message-ID: <20230518060656-mutt-send-email-mst@kernel.org>
Date:   Thu, 18 May 2023 06:09:14 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     zhenwei pi <pizhenwei@...edance.com>
Cc:     Christoph Hellwig <hch@...radead.org>, stefanha@...hat.com,
        jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re: Re: [PATCH v2 1/2] virtio: abstract virtqueue related methods

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