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

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Date:   Thu, 26 Nov 2020 18:19:49 +0000
From:   Annika Wickert <annika.wickert@...ring.de>
To:     Sven Eckelmann <sven@...fation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "b.a.t.m.a.n@...ts.open-mesh.org" <b.a.t.m.a.n@...ts.open-mesh.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] vxlan: Add needed_headroom for lower device

Tested-by: Annika Wickert <aw@...nx.space>
 

On 26.11.20, 13:53, "Sven Eckelmann" <sven@...fation.org> 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>
    ---
     drivers/net/vxlan.c | 1 +
     1 file changed, 1 insertion(+)

    diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
    index 236fcc55a5fd..25b5b5a2dfea 100644
    --- a/drivers/net/vxlan.c
    +++ b/drivers/net/vxlan.c
    @@ -3799,6 +3799,7 @@ static void vxlan_config_apply(struct net_device *dev,
     		dev->gso_max_segs = lowerdev->gso_max_segs;

     		needed_headroom = lowerdev->hard_header_len;
    +		needed_headroom += lowerdev->needed_headroom;

     		max_mtu = lowerdev->mtu - (use_ipv6 ? VXLAN6_HEADROOM :
     					   VXLAN_HEADROOM);
    -- 
    2.29.2