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

zhenwei pi
2023-05-17T08:39:25Z

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...

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