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

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Date:	Mon, 18 Nov 2013 11:51:50 +0100
From:	Willy Tarreau <w@....eu>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Arnaud Ebalard <arno@...isbad.org>,
	Cong Wang <xiyou.wangcong@...il.com>, edumazet@...gle.com,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
	simon.guinot@...uanux.org
Subject: Re: [BUG,REGRESSION?] 3.11.6+,3.12: GbE iface rate drops to few KB/s

Hi Thomas,

On Mon, Nov 18, 2013 at 11:26:01AM +0100, Thomas Petazzoni wrote:
> 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.

No, because my version was even older than the code which introduced this
issue :-)

The main issue is related to something we discussed once ago which surprized
both of us, the use of a Tx timer to release the Tx descriptors. I remember
I considered that it was not a big issue because the flush was also done in
the Rx path (thus on ACKs) but I can't find trace of this code so my analysis
was wrong. Thus we can hit some situations where we fill the descriptors
before filling the link.

Ideally we should have a Tx IRQ. At the very least we should call the tx
refill function in mvneta_poll() I believe. I can try to do it but I'd
rather have the Tx IRQ working instead.

Regards,
Willy

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