netdev - Re: [PATCH 1/2] vxlan: Add needed

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Date:   Mon, 30 Nov 2020 18:34:25 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sven Eckelmann <sven@...fation.org>
Cc:     netdev@...r.kernel.org, b.a.t.m.a.n@...ts.open-mesh.org,
        linux-kernel@...r.kernel.org,
        Annika Wickert <annika.wickert@...ring.de>
Subject: Re: [PATCH 1/2] vxlan: Add needed_headroom for lower device

On Thu, 26 Nov 2020 13:52:46 +0100 Sven Eckelmann wrote:
> It was observed that sending data via batadv over vxlan (on top of
> wireguard) reduced the performance massively compared to raw ethernet or
> batadv on raw ethernet. A check of perf data showed that the
> vxlan_build_skb was calling all the time pskb_expand_head to allocate
> enough headroom for:
> 
>   min_headroom = LL_RESERVED_SPACE(dst->dev) + dst->header_len
>   		+ VXLAN_HLEN + iphdr_len;
> 
> But the vxlan_config_apply only requested needed headroom for:
> 
>   lowerdev->hard_header_len + VXLAN6_HEADROOM or VXLAN_HEADROOM
> 
> So it completely ignored the needed_headroom of the lower device. The first
> caller of net_dev_xmit could therefore never make sure that enough headroom
> was allocated for the rest of the transmit path.
> 
> Cc: Annika Wickert <annika.wickert@...ring.de>
> Signed-off-by: Sven Eckelmann <sven@...fation.org>

Applied both, thanks!