netdev - Re: linux-3.0.18+r8169+ipv4/tcp forwarding = tso/gso weirdness and performance degration

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Date:	Wed, 14 Mar 2012 10:15:14 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Timo Teras <timo.teras@....fi>
Cc:	netdev@...r.kernel.org, Francois Romieu <romieu@...zoreil.com>
Subject: Re: linux-3.0.18+r8169+ipv4/tcp forwarding = tso/gso weirdness and
 performance degration

On Wed, 2012-03-14 at 19:01 +0200, Timo Teras wrote:
> Hi,
> 
> I have a router box running linux-3.0.18 (with grsec patches).
> 
> with the NIC hardware:
> r8169 Gigabit Ethernet driver 2.3LK-NAPI loaded
> r8169 0000:00:09.0: PCI INT A -> GSI 18 (level, low) -> IRQ 18
> r8169 0000:00:09.0: (unregistered net_device): no PCI Express capability
> r8169 0000:00:09.0: eth0: RTL8169sc/8110sc at 0xf82f8000, 00:30:18:ab:6b:54, XID 18000000 IRQ 18
> r8169 Gigabit Ethernet driver 2.3LK-NAPI loaded
> r8169 0000:00:0b.0: PCI INT A -> GSI 19 (level, low) -> IRQ 19
> r8169 0000:00:0b.0: (unregistered net_device): no PCI Express capability
> r8169 0000:00:0b.0: eth1: RTL8169sc/8110sc at 0xf82fa000, 00:30:18:ab:6b:55, XID 18000000 IRQ 19
> r8169 Gigabit Ethernet driver 2.3LK-NAPI loaded
> r8169 0000:00:0c.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
> r8169 0000:00:0c.0: (unregistered net_device): no PCI Express capability
> r8169 0000:00:0c.0: eth2: RTL8169sc/8110sc at 0xf82fc000, 00:30:18:ab:6b:56, XID 18000000 IRQ 16
> 
> This box is working just as a plain IPv4 router (internal RFC1918
> address space) forwarding packets.
> 
> It routes basically from eth2 to multiple vlans over bond0 consisting of eth0 and eth1.
> 
> I have most hw accel stuff turned off, and "ethtool -k eth0" says:
> Offload parameters for eth0:
> rx-checksumming: on
> tx-checksumming: on
> scatter-gather: off
> tcp segmentation offload: off
> udp fragmentation offload: off
> generic segmentation offload: off
> 
> The same applies for all interfaces (except lo).
> 
> However, tcpdump on this box indicates that I'm receiving very
> long (tcp length more than mtu) incoming packets on eth2 implying that
> gso/tso got turned on somehow. eth2 is connected with cross-over cable
> to similar box running a bit older linux box; but gso/tso is turned off
> there too. When dumping simultaneously on the other side, it indicates
> that all packets sent are normal length, and no merging was performed
> earlier (fits mtu 1500).
> 
> So it would appear that the router box somehow insists on doing gso/tso,
> and sadly it will also mess up on the send path (the incoming merged
> packet is forwarded, but sent out short) causing lost segments and
> serious performance degration.
> 
> Any pointers how to next debug/fix/workaround this issue?
> 

You are fighting the wrong side ;)

Here, its GRO doing the aggregation on receiver.

What kind of problems do you experiment because of this ?

ethtool -k eth2


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