From: Daniel Borkmann <daniel@iogearbox•net>
To: Neal Cardwell <ncardwell@google•com>,
Steve Ibanez <sibanez@stanford•edu>
Cc: Netdev <netdev@vger•kernel.org>, Florian Westphal <fw@strlen•de>,
Mohammad Alizadeh <alizadeh@csail•mit.edu>,
Lawrence Brakmo <brakmo@fb•com>
Subject: Re: Linux ECN Handling
Date: Mon, 06 Nov 2017 15:08:54 +0100 [thread overview]
Message-ID: <5A006CF6.1020608@iogearbox.net> (raw)
In-Reply-To: <CADVnQymmMeo=cemUPQCzHpNvFPKCaqY1+VPchmui+HWuCL7CuA@mail.gmail.com>
On 10/24/2017 03:11 AM, Neal Cardwell wrote:
> On Mon, Oct 23, 2017 at 6:15 PM, Steve Ibanez <sibanez@stanford•edu> wrote:
>> Hi All,
>>
>> I upgraded the kernel on all of our machines to Linux
>> 4.13.8-041308-lowlatency. However, I'm still observing the same
>> behavior where the source enters a timeout when the CWND=1MSS and it
>> receives ECN marks.
>>
>> Here are the measured flow rates:
>> <https://drive.google.com/file/d/0B-bt9QS-C3ONT0VXMUt6WHhKREE/view?usp=sharing>
>>
>> Here are snapshots of the packet traces at the sources when they both
>> enter a timeout at t=1.6sec:
>>
>> 10.0.0.1 timeout event:
>> <https://drive.google.com/file/d/0B-bt9QS-C3ONcl9WRnRPazg2ems/view?usp=sharing>
>>
>> 10.0.0.3 timeout event:
>> <https://drive.google.com/file/d/0B-bt9QS-C3ONeDlxRjNXa0VzWm8/view?usp=sharing>
>>
>> Both still essentially follow the same sequence of events that I
>> mentioned earlier:
>> (1) receives an ACK for byte XYZ with the ECN flag set
>> (2) stops sending for RTO_min=300ms
>> (3) sends a retransmission for byte XYZ
>>
>> The cwnd samples reported by tcp_probe still indicate that the sources
>> are reacting to the ECN marks more than once per window. Here are the
>> cwnd samples at the same timeout event mentioned above:
>> <https://drive.google.com/file/d/0B-bt9QS-C3ONdEZQdktpaW5JUm8/view?usp=sharing>
>>
>> Let me know if there is anything else you think I should try.
>
> Sounds like perhaps cwnd is being set to 0 somewhere in this DCTCP
> scenario. Would you be able to add printk statements in
> tcp_init_cwnd_reduction(), tcp_cwnd_reduction(), and
> tcp_end_cwnd_reduction(), printing the IP:port, tp->snd_cwnd, and
> tp->snd_ssthresh?
>
> Based on the output you may be able to figure out where cwnd is being
> set to zero. If not, could you please post the printk output and
> tcpdump traces (.pcap, headers-only is fine) from your tests?
Hi Steve, do you have any updates on your debugging?
> thanks,
> neal
>
next prev parent reply other threads:[~2017-11-06 14:08 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CACJspmLFdy9i8K=TkzXHnofyFMNoJf9HkYE7On8uG+PREc2Dqw@mail.gmail.com>
2017-10-19 12:43 ` Linux ECN Handling Florian Westphal
2017-10-23 22:15 ` Steve Ibanez
2017-10-24 1:11 ` Neal Cardwell
2017-11-06 14:08 ` Daniel Borkmann [this message]
2017-11-06 23:31 ` Steve Ibanez
2017-11-20 7:31 ` Steve Ibanez
2017-11-20 15:05 ` Neal Cardwell
[not found] ` <CADVnQy=q4qBpe0Ymo8dtFTYU_0x0q_XKE+ZvazLQE-ULwu7pQA@mail.gmail.com>
2017-11-20 15:40 ` Eric Dumazet
2017-11-21 5:58 ` Steve Ibanez
2017-11-21 15:01 ` Neal Cardwell
2017-11-21 15:51 ` Yuchung Cheng
2017-11-21 16:20 ` Neal Cardwell
2017-11-21 16:52 ` Eric Dumazet
2017-11-22 3:02 ` Steve Ibanez
2017-11-22 3:46 ` Neal Cardwell
2017-11-27 18:49 ` Steve Ibanez
2017-12-01 16:35 ` Neal Cardwell
2017-12-05 5:22 ` Steve Ibanez
2017-12-05 15:23 ` Neal Cardwell
2017-12-05 19:36 ` Steve Ibanez
2017-12-05 20:04 ` Neal Cardwell
2017-12-19 5:16 ` Steve Ibanez
2017-12-19 15:28 ` Neal Cardwell
2017-12-19 22:00 ` Steve Ibanez
2017-12-20 0:08 ` Neal Cardwell
2017-12-20 19:20 ` Steve Ibanez
2017-12-20 20:17 ` Neal Cardwell
2018-01-02 7:43 ` Steve Ibanez
2018-01-02 16:27 ` Neal Cardwell
2018-01-02 23:57 ` Steve Ibanez
2018-01-03 19:39 ` Neal Cardwell
2018-01-03 22:21 ` Steve Ibanez
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