net_sched: more precise pkt_len computation
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 fda55eca (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> Cc: Jamal Hadi Salim <jhs@mojatatu.com> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: Paolo Valente <paolo.valente@unimore.it> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>
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