netdev - Re: [BUG,REGRESSION?] 3.11.6+,3.12: GbE iface rate drops to few KB/s

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Date:	Wed, 20 Nov 2013 20:26:16 +0100
From:	arno@...isbad.org (Arnaud Ebalard)
To:	Willy Tarreau <w@....eu>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	simon.guinot@...uanux.org, netdev@...r.kernel.org,
	edumazet@...gle.com, Cong Wang <xiyou.wangcong@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [BUG,REGRESSION?] 3.11.6+,3.12: GbE iface rate drops to few KB/s

Hi,

Willy Tarreau <w@....eu> writes:

> first, thanks for all these tests.
>
> On Wed, Nov 20, 2013 at 12:53:43AM +0100, Arnaud Ebalard wrote:
> (...)
>> In the end, here are the conclusions *I* draw from this test session,
>> do not hesitate to correct me:
>> 
>>  - Eric, it seems something changed in linus tree betwen the beginning
>>    of the thread and now, which somehow reduces the effect of the
>>    regression we were seen: I never got back the 256KB/s.
>>  - You revert patch still improves the perf a lot
>>  - It seems reducing MVNETA_TX_DONE_TIMER_PERIOD does not help
>>  - w/ your revert patch, I can confirm that mvneta driver is capable of
>>    doing line rate w/ proper tweak of TCP send window (256KB instead of
>>    4M)
>>  - It seems I will I have to spend some time on the SATA issues I
>>    previously thought were an artefact of not cleaning my tree during a
>>    debug session [1], i.e. there is IMHO an issue.
>
> Could you please try Eric's patch that was just merged into Linus' tree
> if it was not yet in the kernel you tried :
>
>   98e09386c0e  tcp: tsq: restore minimal amount of queueing

I have it in my quilt set.


> For me it restored the original performance (I saturate the Gbps with
> about 7 concurrent streams).
>
> Further, I wrote the small patch below for mvneta. I'm not sure it's
> smp-safe but it's a PoC. In mvneta_poll() which currently is only called
> upon Rx interrupt, it tries to flush all possible remaining Tx descriptors
> if any. That significantly improved my transfer rate, now I easily achieve
> 1 Gbps using a single TCP stream on the mirabox. Not tried on the AX3 yet.
>
> It also increased the overall connection rate by 10% on empty HTTP responses
> (small packets), very likely by reducing the dead time between some segments!
>
> You'll probably want to give it a try, so here it comes.

hehe, I was falling short of patches to test tonight ;-) I will give it
a try now.

Cheers,

a+
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