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 09:13:28 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	Simon Guinot <simon.guinot@...uanux.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	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, 2013-11-18 at 08:54 -0800, Stephen Hemminger wrote:
> On Mon, 18 Nov 2013 11:44:48 +0100
> Simon Guinot <simon.guinot@...uanux.org> wrote:

> > c9eeec26 tcp: TSQ can use a dynamic limit
> > 
> 
> But without that patch there was a performance regression for high speed
> interfaces whihc was caused by TSQ. 10G performance dropped to 8G

Yes, this made sure we could feed more than 2 TSO packets on TX ring.

But decreasing minimal amount of queuing from 128KB to ~1ms of the
current rate did not please NIC which can have a big delay between
ndo_start_xmit() and actual skb freeing (TX completion)

So
http://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=98e09386c0ef4dfd48af7ba60ff908f0d525cdee

restored this minimal amount of buffering, and let the bigger amount for
40Gb NICs ;)



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