Re: [PATCH net-next v5 12/15] virtio-net: support AF_XDP zc tx

From: Jason Wang <jasowang@redhat.com>
To: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: "Song Liu" <songliubraving@fb.com>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Yonghong Song" <yhs@fb.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	netdev@vger.kernel.org, "Björn Töpel" <bjorn@kernel.org>,
	"dust.li" <dust.li@linux.alibaba.com>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>,
	"Jakub Kicinski" <kuba@kernel.org>,
	bpf@vger.kernel.org, virtualization@lists.linux-foundation.org,
	"David S. Miller" <davem@davemloft.net>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>
Subject: Re: [PATCH net-next v5 12/15] virtio-net: support AF_XDP zc tx
Date: Wed, 16 Jun 2021 20:51:41 +0800	[thread overview]
Message-ID: <f81775f8-7df9-5ca0-0bd2-99c86786fe78@redhat.com> (raw)
In-Reply-To: <1623838784.446967-1-xuanzhuo@linux.alibaba.com>

在 2021/6/16 下午6:19, Xuan Zhuo 写道:
>>> + * In this way, even if xsk has been unbundled with rq/sq, or a new xsk and
>>> + * rq/sq  are bound, and a new virtnet_xsk_ctx_head is created. It will not
>>> + * affect the old virtnet_xsk_ctx to be recycled. And free all head and ctx when
>>> + * ref is 0.
>> This looks complicated and it will increase the footprint. Consider the
>> performance penalty and the complexity, I would suggest to use reset
>> instead.
>>
>> Then we don't need to introduce such context.
> I don't like this either. It is best if we can reset the queue, but then,
> according to my understanding, the backend should also be supported
> synchronously, so if you don't update the backend synchronously, you can't use
> xsk.

Yes, actually, vhost-net support per vq suspending. The problem is that 
we're lacking a proper API at virtio level.

Virtio-pci has queue_enable but it forbids writing zero to that.

>
> I don’t think resetting the entire dev is a good solution. If you want to bind
> xsk to 10 queues, you may have to reset the entire device 10 times. I don’t
> think this is a good way. But the current spec does not support reset single
> queue, so I chose the current solution.
>
> Jason, what do you think we are going to do? Realize the reset function of a
> single queue?

Yes, it's the best way. Do you want to work on that?

We can start from the spec patch, and introduce it as basic facility and 
implement it in the PCI transport first.

Thanks

>
> Looking forward to your reply!!!
>
> Thanks
>

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