netdev - Re: [PATCH v5 20/22] virtio_net: set the default max ring num

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Date:   Mon, 21 Feb 2022 11:40:13 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org
Subject: Re: [PATCH v5 20/22] virtio_net: set the default max ring num


在 2022/2/17 下午5:30, Xuan Zhuo 写道:
> On Thu, 17 Feb 2022 15:21:26 +0800, Jason Wang <jasowang@...hat.com> wrote:
>> On Wed, Feb 16, 2022 at 3:52 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>>> On Wed, 16 Feb 2022 12:14:31 +0800, Jason Wang <jasowang@...hat.com> wrote:
>>>> On Mon, Feb 14, 2022 at 4:14 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>>>>> Sets the default maximum ring num based on virtio_set_max_ring_num().
>>>>>
>>>>> The default maximum ring num is 1024.
>>>> Having a default value is pretty useful, I see 32K is used by default for IFCVF.
>>>>
>>>> Rethink this, how about having a different default value based on the speed?
>>>>
>>>> Without SPEED_DUPLEX, we use 1024. Otherwise
>>>>
>>>> 10g 4096
>>>> 40g 8192
>>> We can define different default values of tx and rx by the way. This way I can
>>> just use it in the new interface of find_vqs().
>>>
>>> without SPEED_DUPLEX:  tx 512 rx 1024
>>>
>> Any reason that TX is smaller than RX?
>>
> I've seen some NIC drivers with default tx smaller than rx.


Interesting, do they use combined channels?


>
> One problem I have now is that inside virtnet_probe, init_vqs is before getting
> speed/duplex. I'm not sure, can the logic to get speed/duplex be put before
> init_vqs? Is there any risk?
>
> Can you help me?


The feature has been negotiated during probe(), so I don't see any risk.

Thanks


>
> Thanks.
>
>> Thanks
>>
>>> Thanks.
>>>
>>>
>>>> etc.
>>>>
>>>> (The number are just copied from the 10g/40g default parameter from
>>>> other vendors)
>>>>
>>>> Thanks
>>>>
>>>>> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>>>>> ---
>>>>>   drivers/net/virtio_net.c | 4 ++++
>>>>>   1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>>> index a4ffd7cdf623..77e61fe0b2ce 100644
>>>>> --- a/drivers/net/virtio_net.c
>>>>> +++ b/drivers/net/virtio_net.c
>>>>> @@ -35,6 +35,8 @@ module_param(napi_tx, bool, 0644);
>>>>>   #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
>>>>>   #define GOOD_COPY_LEN  128
>>>>>
>>>>> +#define VIRTNET_DEFAULT_MAX_RING_NUM 1024
>>>>> +
>>>>>   #define VIRTNET_RX_PAD (NET_IP_ALIGN + NET_SKB_PAD)
>>>>>
>>>>>   /* Amount of XDP headroom to prepend to packets for use by xdp_adjust_head */
>>>>> @@ -3045,6 +3047,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>>>>>                          ctx[rxq2vq(i)] = true;
>>>>>          }
>>>>>
>>>>> +       virtio_set_max_ring_num(vi->vdev, VIRTNET_DEFAULT_MAX_RING_NUM);
>>>>> +
>>>>>          ret = virtio_find_vqs_ctx(vi->vdev, total_vqs, vqs, callbacks,
>>>>>                                    names, ctx, NULL);
>>>>>          if (ret)
>>>>> --
>>>>> 2.31.0
>>>>>