netdev - Re: [PATCH net-next] net-gro: Prepare GRO stack for the upcoming tunneling support

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Date:	Sun, 08 Dec 2013 19:04:23 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jerry Chu <hkchu@...gle.com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net-gro: Prepare GRO stack for the upcoming
 tunneling support

On Mon, 2013-12-09 at 10:48 +0800, Jerry Chu wrote:

> Not sure why ingress qdisc - it seems that qdisc_pkt_len_init() is only called
> by the egress path (__dev_xmit_skb())
> .

Yeah, Qdisc was meant to be used for egress.

Then to get qdisc for ingress, we use IFB to reinject packets through
the qdisc layer.

Sample of script :

ETH=eth0
IFB=ifb0
RTT_HALF=50ms
REORDER=1500us

modprobe ifb
ip link set dev $IFB up

tc qdisc add dev $ETH ingress 2>/dev/null

tc filter add dev $ETH parent ffff: \
   protocol ip u32 match u32 0 0 flowid 1:1 action mirred egress \
   redirect dev $IFB

tc qdisc del dev $IFB root 2>/dev/null
tc qdisc add dev $IFB root netem limit 100000 delay $RTT_HALF $REORDER 



> Strange why is it the business of *netif_receive_skb*() to set the
> transport header
> before IP has a chance to parse the IP hdr?
> 

Maybe you should use git blame ;)



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