netdev - Re: [PATCH] net: tun: fix tun_xdp_one() for IFF

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Message-ID: <2433592d2b26deec33336dd3e83acfd273b0cf30.camel@infradead.org>
Date:   Mon, 21 Jun 2021 15:50:45 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Jason Wang <jasowang@...hat.com>, netdev <netdev@...r.kernel.org>
Cc:     Eugenio Pérez <eperezma@...hat.com>
Subject: Re: [PATCH] net: tun: fix tun_xdp_one() for IFF_TUN mode

On Mon, 2021-06-21 at 11:52 +0100, David Woodhouse wrote:
> 
> Firstly, I don't think I can set IFF_VNET_HDR on the tun device after
> opening it. So my model of "open the tun device, then *see* if we can
> use vhost to accelerate it" doesn't work.
> 
> I tried setting VHOST_NET_F_VIRTIO_NET_HDR in the vhost features
> instead, but that gives me a weird failure mode where it drops around
> half the incoming packets, and I haven't yet worked out why.

FWIW that problem also goes away if I set TUNSNDBUF and avoid the XDP
data path.

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