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

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Message-ID: <20131118104448.GI16823@kw.sim.vm.gnt>
Date:	Mon, 18 Nov 2013 11:44:48 +0100
From:	Simon Guinot <simon.guinot@...uanux.org>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Willy Tarreau <w@....eu>, Arnaud Ebalard <arno@...isbad.org>,
	Cong Wang <xiyou.wangcong@...il.com>, edumazet@...gle.com,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
	Vincent Donnefort <vdonnefort@...il.com>
Subject: Re: [BUG,REGRESSION?] 3.11.6+,3.12: GbE iface rate drops to few KB/s

On Mon, Nov 18, 2013 at 11:26:01AM +0100, Thomas Petazzoni wrote:
> Willy, All,
> 
> On Sun, 17 Nov 2013 15:19:40 +0100, Willy Tarreau wrote:
> 
> > On Wed, Nov 13, 2013 at 08:22:57AM +0100, Willy Tarreau wrote:
> > > On Tue, Nov 12, 2013 at 04:34:24PM +0100, Arnaud Ebalard wrote:
> > > > Can you give a pre-3.11.7 kernel a try if you find the time? I
> > > > started working on RN102 during 3.10-rc cycle but do not remember
> > > > if I did the first preformance tests on 3.10 or 3.11. And if you
> > > > find more time, 3.11.7 would be nice too ;-)
> > > 
> > > Still have not found time for this but I observed something
> > > intriguing which might possibly match your experience : if I use
> > > large enough send buffers on the mirabox and receive buffers on the
> > > client, then the traffic drops for objects larger than 1 MB. I have
> > > quickly checked what's happening and it's just that there are
> > > pauses of up to 8 ms between some packets when the TCP send window
> > > grows larger than about 200 kB. And since there are no drops, there
> > > is no reason for the window to shrink. I suspect it's exactly
> > > related to the issue explained by Eric about the timer used to
> > > recycle the Tx descriptors. However last time I checked, these ones
> > > were also processed in the Rx path, which means that the ACKs that
> > > flow back should have had the same effect as a Tx IRQ (unless I'd
> > > use asymmetric routing, which was not the case). So there might be
> > > another issue. Ah, and it only happens with GSO.
> 
> I haven't read the entire discussion yet, but do you guys have
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/clk/mvebu?id=1022c75f5abd3a3b25e679bc8793d21bedd009b4
> applied? It got merged recently, and it fixes a number of networking
> problems on Armada 370.
> 
> I've added Simon Guinot in Cc, who is the author of this patch.

I don't think it is related. We also have noticed a huge performance
regression. Reverting the following patch restores the rate:

c9eeec26 tcp: TSQ can use a dynamic limit

I don't understand why...

Regards,

Simon

> 
> Best regards,
> 
> Thomas
> -- 
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com

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