netdev - Re: Bonding gigabit and fast?

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Message-Id: <200812162012.29811.tvrtko@ursulin.net>
Date:	Tue, 16 Dec 2008 20:12:29 +0000
From:	"Tvrtko A. Ursulin" <tvrtko@...ulin.net>
To:	Chris Snook <csnook@...hat.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Bonding gigabit and fast?

On Tuesday 16 December 2008 19:54:29 Chris Snook wrote:
> > When serving data from the machine I get 13.7 MB/s aggregated while with
> > a single slave (so bond still active) I get 5.6 MB/s for gigabit and 9.1
> > MB/s for fast. Yes, that's not a typo - fast ethernet is faster than
> > gigabit.
>
> That would qualify as something very wrong with your gigabit card.  What do
> you get when bonding is completely disabled?

With same testing methology (ie. serving from Samba to CIFS) it averages to 
around 10 Mb/s, so somewhat faster than when bonded but still terribly 
unstable. Problem is I think it was much better under older kernels. I wrote 
about it before:

http://lkml.org/lkml/2008/11/20/418
http://bugzilla.kernel.org/show_bug.cgi?id=6796

Stephen thinks it may be limited PCI bandwith, but the fact that I get double 
speed in the opposite direction and that slow direction was previously 
roughly double of what it is now, makes me suspicious that there is a 
regression here somewhere.

> > That is actually another problem I was trying to get to the bottom of for
> > some time. Gigabit adapter is skge in a PCI slot and outgoing bandwith
> > oscillates a lot during transfer, much more than on 8139too which is both
> > stable and faster.
>
> The gigabit card might be sharing a PCI bus with your disk controller, so
> swapping which slots the cards are in might make gigabit work faster, but
> it sounds more like the driver is doing something stupid with interrupt
> servicing.

Dang you are right, they really do share the same interrupt. And I have 
nowhere else to move that card since it is a single PCI slot. Interestingly, 
fast ethernet (eth0) generates double number of interrupts than gigabit 
(eth1) and SATA combined.

>From powertop:

Top causes for wakeups:
  65.5% (11091.1)       <interrupt> : eth0
  32.9% (5570.5)       <interrupt> : sata_sil, eth1

Tvrtko
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