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

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Date:   Thu, 18 May 2023 08:47:22 +0800
From:   zhenwei pi <pizhenwei@...edance.com>
To:     "Michael S. Tsirkin" <mst@...hat.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 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

> 
>> 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