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

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Message-ID: <21e53c2b-6677-fc9a-0771-e895da1c257f@redhat.com>
Date:   Thu, 15 Mar 2018 16:39:25 +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