From: David Miller <davem@davemloft.net>
To: herbert@gondor.apana.org.au
Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org
Subject: Re: [PATCH RFC] net: tcp: GRO should be ECN friendly
Date: Mon, 06 Aug 2012 13:41:18 -0700 (PDT) [thread overview]
Message-ID: <20120806.134118.2197594378586931190.davem@davemloft.net> (raw)
In-Reply-To: <20120806090150.GB18425@gondor.apana.org.au>
From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Mon, 6 Aug 2012 17:01:50 +0800
> On Mon, Aug 06, 2012 at 10:34:50AM +0200, Eric Dumazet wrote:
>> From: Eric Dumazet <edumazet@google.com>
>>
>> While doing TCP ECN tests, I discovered GRO was reordering packets if it
>> receives one packet with CE set, while previous packets in same NAPI run
>> have ECT(0) for the same flow :
>>
>> 09:25:25.857620 IP (tos 0x2,ECT(0), ttl 64, id 27893, offset 0, flags
>> [DF], proto TCP (6), length 4396)
>> 172.30.42.19.54550 > 172.30.42.13.44139: Flags [.], seq
>> 233801:238145, ack 1, win 115, options [nop,nop,TS val 3397779 ecr
>> 1990627], length 4344
>>
>> 09:25:25.857626 IP (tos 0x3,CE, ttl 64, id 27892, offset 0, flags [DF],
>> proto TCP (6), length 1500)
>> 172.30.42.19.54550 > 172.30.42.13.44139: Flags [.], seq
>> 232353:233801, ack 1, win 115, options [nop,nop,TS val 3397779 ecr
>> 1990627], length 1448
>>
>> 09:25:25.857638 IP (tos 0x0, ttl 64, id 34581, offset 0, flags [DF],
>> proto TCP (6), length 64)
>> 172.30.42.13.44139 > 172.30.42.19.54550: Flags [.], cksum 0xac8f
>> (incorrect -> 0xca69), ack 232353, win 1271, options [nop,nop,TS val
>> 1990627 ecr 3397779,nop,nop,sack 1 {233801:238145}], length 0
>>
>> We have two problems here :
>>
>> 1) GRO reorders packets
>>
>> If NIC gave packet1, then packet2, which happen to be from "different
>> flows" GRO feeds stack with packet2, then packet1. I have yet to
>> understand how to solve this problem.
>>
>> 2) GRO is not ECN friendly
>>
>> Delivering packets out of order makes TCP stack not as fast as it could
>> be.
>>
>> In this patch I suggest we make the tos test not part of the 'same_flow'
>> determination, but part of the 'should flush' logic
>>
>> Signed-off-by: Eric Dumazet <edumazet@google.com>
>
> Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
>
> Good catch, thanks Eric!
Applied to net-next, thanks Eric.
prev parent reply other threads:[~2012-08-06 20:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-06 8:34 [PATCH RFC] net: tcp: GRO should be ECN friendly Eric Dumazet
2012-08-06 9:01 ` Herbert Xu
2012-08-06 20:41 ` David Miller [this message]
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