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

[Stephen Hemminger]

On Mon, 18 Nov 2013 11:44:48 +0100
Simon Guinot <simon.guinot at sequanux.org> wrote:

> 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
> 

But without that patch there was a performance regression for high speed
interfaces whihc was caused by TSQ. 10G performance dropped to 8G