Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK_SEQPACKET support

From: Stefano Garzarella <sgarzare@redhat.com>
To: Arseny Krasnov <arseny.krasnov@kaspersky.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Jorgen Hansen <jhansen@vmware.com>,
	Colin Ian King <colin.king@canonical.com>,
	Andra Paraschiv <andraprs@amazon.com>,
	Norbert Slusarek <nslusarek@gmx.net>,
	Alexander Popov <alex.popov@linux.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stsp2@yandex.ru" <stsp2@yandex.ru>,
	"oxffffaa@gmail.com" <oxffffaa@gmail.com>
Subject: Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK_SEQPACKET support
Date: Thu, 22 Apr 2021 12:48:13 +0200	[thread overview]
Message-ID: <20210422104813.e2p4wzuk2ahw7af7@steredhat> (raw)
In-Reply-To: <bc649d1b-80d8-835c-6f47-8a7d402dd0b7@kaspersky.com>

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