linux-kernel - Re: TCP reaching to maximum throughput after a long time

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Date:	Tue, 12 Apr 2016 20:08:06 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"Machani, Yaniv" <yanivma@...com>, netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	open list <linux-kernel@...r.kernel.org>,
	"Kama, Meirav" <meiravk@...com>
Subject: Re: TCP reaching to maximum throughput after a long time

On Tue, Apr 12, 2016 at 2:40 PM, Ben Greear <greearb@...delatech.com> wrote:
> On 04/12/2016 01:29 PM, Eric Dumazet wrote:
>>
>> On Tue, 2016-04-12 at 13:23 -0700, Ben Greear wrote:
>>
>>> It worked well enough for years that I didn't even know other algorithms
>>> were
>>> available.  It was broken around 4.0 time, and I reported it to the list,
>>> and no one seemed to really care enough to do anything about it.  I
>>> changed
>>> to reno and ignored the problem as well.
>>>
>>> It is trivially easy to see the regression when using ath10k NIC, and
>>> from this email
>>> thread, I guess other NICs have similar issues.
>>
>>
>> Since it is so trivial, why don't you start a bisection ?
>
>
> I vaguely remember doing a bisect, but I can't find any email about
> that, so maybe I didn't.  At any rate, it is somewhere between 3.17 and 4.0.
> From memory, it was between 3.19 and 4.0, but I am not certain of that.
>
> Neil's suggestion, from the thread below, is that it was likely:  "605ad7f
> tcp: refine TSO autosizing"
>
> Here is previous email thread:
>
> https://www.mail-archive.com/netdev@vger.kernel.org/msg80803.html
>
> This one has a link to a pcap I made at the time:
>
> https://www.mail-archive.com/netdev@vger.kernel.org/msg80890.html
based on the prev thread I propose we disable hystart ack-train. It is
brittle under various circumstances. We've disabled that at Google for
years.

>
>>
>> I asked a capture, I did not say ' switch to Reno or whatever ', right ?
>>
>> Guessing is nice, but investigating and fixing is better.
>>
>> Do not assume that nothing can be done, please ?
>
>
> Thanks,
> Ben
>
> --
> Ben Greear <greearb@...delatech.com>
> Candela Technologies Inc  http://www.candelatech.com
>