netdev - Re: Slow speed of tcp connections in a network namespace

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Date:	Sun, 30 Dec 2012 01:07:14 +0400
From:	Andrew Vagin <avagin@...allels.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	<netdev@...r.kernel.org>, <vvs@...allels.com>,
	Michał Mirosław <mirq-linux@...e.qmqm.pl>
Subject: Re: Slow speed of tcp connections in a network namespace

On Sat, Dec 29, 2012 at 12:20:07PM -0800, Eric Dumazet wrote:
> On Sun, 2012-12-30 at 00:08 +0400, Andrew Vagin wrote:
> > On Sat, Dec 29, 2012 at 11:41:02AM -0800, Eric Dumazet wrote:
> > > On Sat, 2012-12-29 at 19:58 +0100, Eric Dumazet wrote:
> > > > Le samedi 29 décembre 2012 à 09:40 -0800, Eric Dumazet a écrit :
> > > > 
> > > > > 
> > > > > Please post your new tcpdump then ;)
> > > > > 
> > > > > also post "netstat -s" from root and test ns after your wgets
> > > > 
> > > > Also try following bnx2 patch.
> > > > 
> > > > It should help GRO / TCP coalesce
> > > > 
> > > > bnx2 should be the last driver not using skb head_frag
> > 
> > I don't have access to the host. I'm going to test your patch tomorrow.
> > Thanks.
> > 
> > > 
> > > And of course, you should make sure all your bnx2 interrupts are handled
> > > by the same cpu.
> > All bnx interrupts are handled on all cpus. They are handled on the same
> > cpu, if a kernel is booted with msi_disable=1.
> > 
> > Is it right, that a received window will be less, if packets are not sorted?
> > Looks like a bug.
> > 
> > I want to say, that probably it works correctly, if packets are sorted.
> > But I think if packets are not sorted, it should work with the same
> > speed, cpu load and memory consumption may be a bit more.
> 
> Without veth, it doesnt really matter that IRQ are spread on multiple
> cpus, because packets are handled in NAPI, and only one cpu runs the
> eth0 NAPI handler at one time.
> 
> But as soon as packets are queued (by netif_rx()) for 'later'
> processing, you can have dramatic performance decrease.
> 
> Thats why you really should make sure IRQ on your eth0 device
> are handled by a single cpu.
> 
> It will help to get better performance in most cases.

I understand this fact, but so big difference looks strange for me.

Default configuration (with the bug):
# cat /proc/interrupts  | grep eth0
  68:      10187      10188      10187      10023      10190      10185
10187      10019   PCI-MSI-edge      eth0

> 
> echo 1 >/proc/irq/*/eth0/../smp_affinity

This doesn't help.

I tryed echo 0 > /proc/irq/68/smp_affinity_list. This doesn't help too.

> 
> If it doesnt work, you might try instead :
> 
> echo 1 >/proc/irq/default_smp_affinity
> <you might need to reload bnx2 module, or ifdown/ifup eth0 >

This helps, and the bug are not reproduced in this case.

# cat /proc/interrupts  | grep eth0
  68:      60777          0          0          0          0          0
0          0   PCI-MSI-edge      eth0

Thanks.
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