[PATCH 1/2] vxlan: Add needed_headroom for lower device

[PATCH 1/2] vxlan: Add needed_headroom for lower device

[Sven Eckelmann]

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@exaring.de>
Signed-off-by: Sven Eckelmann <sven@narfation.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

[PATCH 2/2] vxlan: Copy needed_tailroom from lowerdev

[Sven Eckelmann]

While vxlan doesn't need any extra tailroom, the lowerdev might need it. In
that case, copy it over to reduce the chance for additional (re)allocations
in the transmit path.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 drivers/net/vxlan.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 25b5b5a2dfea..44bb02122526 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -3801,6 +3801,8 @@ static void vxlan_config_apply(struct net_device *dev,
 		needed_headroom = lowerdev->hard_header_len;
 		needed_headroom += lowerdev->needed_headroom;
 
+		dev->needed_tailroom = lowerdev->needed_tailroom;
+
 		max_mtu = lowerdev->mtu - (use_ipv6 ? VXLAN6_HEADROOM :
 					   VXLAN_HEADROOM);
 		if (max_mtu < ETH_MIN_MTU)
-- 
2.29.2

Re: [PATCH 1/2] vxlan: Add needed_headroom for lower device

[Annika Wickert]

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

On 26.11.20, 13:53, "Sven Eckelmann" <sven@narfation.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@exaring.de>
    Signed-off-by: Sven Eckelmann <sven@narfation.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

Re: [PATCH 1/2] vxlan: Add needed_headroom for lower device

[Jakub Kicinski]

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@exaring.de>
> Signed-off-by: Sven Eckelmann <sven@narfation.org>

Applied both, thanks!