[Codel] [RFC PATCH] codel: ecn mark at target

[Eric Dumazet]

On Sun, 2012-08-05 at 19:26 +0200, Eric Dumazet wrote:

> It could be a flaw in linux implementation, I admit we had so many bugs
> that it could very well be still buggy.

And at first glance, the following tcpdump seems suspect : We can see
all ACK are delayed by about 40 ms

19:30:54.367739 IP (tos 0x3,CE, ttl 64, id 52620, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [.], seq 156841:158289, ack 1, win 115, options [nop,nop,TS val 3115533 ecr 111212487], length 1448
19:30:54.406063 IP (tos 0x0, ttl 64, id 62099, offset 0, flags [DF], proto TCP (6), length 52)
    172.30.42.18.50103 > 172.30.42.19.50341: Flags [.E], cksum 0xac88 (incorrect -> 0xe2b7), ack 158289, win 551, options [nop,nop,TS val 111212491 ecr 3115533], length 0

19:30:54.407212 IP (tos 0x3,CE, ttl 64, id 52621, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [P.W], seq 158289:159737, ack 1, win 115, options [nop,nop,TS val 3115573 ecr 111212491], length 1448
19:30:54.446057 IP (tos 0x0, ttl 64, id 62100, offset 0, flags [DF], proto TCP (6), length 52)
    172.30.42.18.50103 > 172.30.42.19.50341: Flags [.E], cksum 0xac88 (incorrect -> 0xdce3), ack 159737, win 551, options [nop,nop,TS val 111212495 ecr 3115573], length 0



19:30:54.448209 IP (tos 0x3,CE, ttl 64, id 52622, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [.W], seq 159737:161185, ack 1, win 115, options [nop,nop,TS val 3115613 ecr 111212495], length 1448
19:30:54.486057 IP (tos 0x0, ttl 64, id 62101, offset 0, flags [DF], proto TCP (6), length 52)
    172.30.42.18.50103 > 172.30.42.19.50341: Flags [.E], cksum 0xac88 (incorrect -> 0xd70f), ack 161185, win 551, options [nop,nop,TS val 111212499 ecr 3115613], length 0

19:30:54.487443 IP (tos 0x3,CE, ttl 64, id 52623, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [.W], seq 161185:162633, ack 1, win 115, options [nop,nop,TS val 3115653 ecr 111212499], length 1448
19:30:54.526069 IP (tos 0x0, ttl 64, id 62102, offset 0, flags [DF], proto TCP (6), length 52)
    172.30.42.18.50103 > 172.30.42.19.50341: Flags [.E], cksum 0xac88 (incorrect -> 0xd13b), ack 162633, win 551, options [nop,nop,TS val 111212503 ecr 3115653], length 0

19:30:54.527241 IP (tos 0x2,ECT(0), ttl 64, id 52624, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [.W], seq 162633:164081, ack 1, win 115, options [nop,nop,TS val 3115693 ecr 111212503], length 1448
19:30:54.566049 IP (tos 0x0, ttl 64, id 62103, offset 0, flags [DF], proto TCP (6), length 52)
    172.30.42.18.50103 > 172.30.42.19.50341: Flags [.], cksum 0xac88 (incorrect -> 0xcba7), ack 164081, win 551, options [nop,nop,TS val 111212507 ecr 3115693], length 0

19:30:54.567809 IP (tos 0x3,CE, ttl 64, id 52625, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [.], seq 164081:165529, ack 1, win 115, options [nop,nop,TS val 3115733 ecr 111212507], length 1448
19:30:54.606067 IP (tos 0x0, ttl 64, id 62104, offset 0, flags [DF], proto TCP (6), length 52)
    172.30.42.18.50103 > 172.30.42.19.50341: Flags [.E], cksum 0xac88 (incorrect -> 0xc593), ack 165529, win 551, options [nop,nop,TS val 111212511 ecr 3115733], length 0
19:30:54.607088 IP (tos 0x2,ECT(0), ttl 64, id 52626, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [.W], seq 165529:166977, ack 1, win 115, options [nop,nop,TS val 3115773 ecr 111212511], length 1448
19:30:54.646056 IP (tos 0x0, ttl 64, id 62105, offset 0, flags [DF], proto TCP (6), length 52)
    172.30.42.18.50103 > 172.30.42.19.50341: Flags [.], cksum 0xac88 (incorrect -> 0xbfff), ack 166977, win 551, options [nop,nop,TS val 111212515 ecr 3115773], length 0
19:30:54.648105 IP (tos 0x3,CE, ttl 64, id 52627, offset 0, flags [DF], proto TCP (6), length 1500)
    172.30.42.19.50341 > 172.30.42.18.50103: Flags [.], seq 166977:168425, ack 1, win 115, options [nop,nop,TS val 3115813 ecr 111212515], length 1448