linux-kernel - Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK

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Date:   Thu, 22 Apr 2021 12:48:13 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseny Krasnov <arseny.krasnov@...persky.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Colin Ian King <colin.king@...onical.com>,
        Andra Paraschiv <andraprs@...zon.com>,
        Norbert Slusarek <nslusarek@....net>,
        Alexander Popov <alex.popov@...ux.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK_SEQPACKET
 support

On Thu, Apr 22, 2021 at 01:29:54PM +0300, Arseny Krasnov wrote:
>
>On 22.04.2021 13:02, Stefano Garzarella wrote:
>> On Thu, Apr 22, 2021 at 12:40:17PM +0300, Arseny Krasnov wrote:
>>> On 22.04.2021 11:46, Stefano Garzarella wrote:
>>>> On Wed, Apr 21, 2021 at 06:06:28PM +0300, Arseny Krasnov wrote:
>>>>> Thank You, i'll prepare next version. Main question is: does this
>>>>> approach(no SEQ_BEGIN, SEQ_END, 'msg_len' and 'msg_id') considered
>>>>> good? In this case it will be easier to prepare final version, because
>>>>> is smaller and more simple than previous logic. Also patch to spec
>>>>> will be smaller.
>>>> Yes, it's definitely much better than before.
>>>>
>>>> The only problem I see is that we add some overhead per fragment
>>>> (header). We could solve that with the mergeable buffers that Jiang is
>>>> considering for DGRAM.
>>> If we are talking about receive, i think, i can reuse merge logic for
>> Yep, for TX the guest can potentially enqueue a big buffer.
>> Maybe it's still worth keeping a maximum size and fragmenting as we do
>> now.
>>
>>> stream sockets, the only difference is that buffers are mergeable
>>> until previous EOR(e.g. previous message) bit is found in rx queue.
>>>
>> I got a little lost.
>> Can you elaborate more?
>
>I'm talking about 'virtio_transport_recv_enqueue()': it tries to copy
>
>data of new packet to buffer of tail packet in rx queue. In case of
>
>SEQPACKET i can reuse it, just adding logic that check EOR bit of
>
>tail packet.

This might be a good idea.
It doesn't save us the transmitted header though, but at least it saves 
us from queuing it.
Even if with SEQPACKET I don't expect small packets, since it's the 
driver that divides them and I think it does everything to use the 
maximum available.

Instead the mergeable buffers I was referring to are based on the 
virito-net feature VIRTIO_NET_F_MRG_RXBUF.
Jiang is investigating whether we can reuse them for DGRAM.

Thanks,
Stefano