netdev - Re: [PATCH net-next] tuntap: XDP

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Message-ID: <9b895dba-71bf-8053-610b-83ecb6d36879@redhat.com>
Date:   Fri, 16 Mar 2018 14:46:22 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] tuntap: XDP_TX can use native XDP

On 2018年03月15日 21:32, Michael S. Tsirkin wrote:
> On Thu, Mar 15, 2018 at 04:39:25PM +0800, Jason Wang wrote:
>>
>> On 2018年03月14日 11:37, Michael S. Tsirkin wrote:
>>>>    			return NULL;
>>>>    		case XDP_TX:
>>>> -			xdp_xmit = true;
>>>> -			/* fall through */
>>>> +			get_page(alloc_frag->page);
>>>> +			alloc_frag->offset += buflen;
>>>> +			if (tun_xdp_xmit(tun->dev, &xdp))
>>>> +				goto err_redirect;
>>>> +			tun_xdp_flush(tun->dev);
>>> Why do we have to flush here though?
>>> It might be a good idea to document the reason in a code comment.
>>>
>> ndo_xdp_xmit() does not touch doorbell, so we need a ndo_xdp_flush() here.
>> It's the assumption of XDP API I think, so not sure it's worth to mention it
>> here.
>>
>> Thanks
> Can't one flush we called after multiple xmit calls?

We can and could be another patch on top. But I want to unify it with 
the batching of XDP_REDIRECT by e.g let vhost submit more than one 
packets through msg.control in sendmsg().

Thanks