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

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Message-ID: <f16b8f56-8890-a4ae-0108-ff5667350fbc@bytedance.com>
Date:   Thu, 18 May 2023 19:01:40 +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: Re: [PATCH v2 1/2] virtio: abstract virtqueue related
 methods



On 5/18/23 18:09, Michael S. Tsirkin wrote:
> 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.
> 

OK, I'd drop this series.

Cc Jason & Stefan.


-- 
zhenwei pi