Re: [PATCH v2 net-next] net_sched: more precise pkt_len computation

[David Miller <davem@davemloft.net>]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 10 Jan 2013 14:36:42 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> One long standing problem with TSO/GSO/GRO packets is that skb->len
> doesn't represent a precise amount of bytes on wire.
> 
> Headers are only accounted for the first segment.
> For TCP, thats typically 66 bytes per 1448 bytes segment missing,
> an error of 4.5 % for normal MSS value.
> 
> As consequences :
> 
> 1) TBF/CBQ/HTB/NETEM/... can send more bytes than the assigned limits.
> 2) Device stats are slightly under estimated as well.
> 
> Fix this by taking account of headers in qdisc_skb_cb(skb)->pkt_len
> computation.
> 
> Packet schedulers should use qdisc pkt_len instead of skb->len for their
> bandwidth limitations, and TSO enabled devices drivers could use pkt_len
> if their statistics are not hardware assisted, and if they don't scratch
> skb->cb[] first word.
> 
> Both egress and ingress paths work, thanks to commit fda55eca5a
> (net: introduce skb_transport_header_was_set()) : If GRO built
> a GSO packet, it also set the transport header for us.
> 
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Looks good, applied, thanks Eric.