netdev - Re: [PATCH 2.6.30-rc4] r8169: avoid losing MSI interrupts

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Message-Id: <200905231850.14725.mb@bu3sch.de>
Date:	Sat, 23 May 2009 18:50:14 +0200
From:	Michael Buesch <mb@...sch.de>
To:	David Dillow <dave@...dillows.org>
Cc:	Michael Riepe <michael.riepe@...glemail.com>,
	Francois Romieu <romieu@...zoreil.com>,
	Rui Santos <rsantos@...popie.com>,
	Michael Büker <m.bueker@...lin.de>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2.6.30-rc4] r8169: avoid losing MSI interrupts

On Saturday 23 May 2009 18:46:13 David Dillow wrote:
> On Sat, 2009-05-23 at 18:12 +0200, Michael Riepe wrote:
> > If I use two connections (iperf -P2) and nail iperf to both threads of a
> > single core with taskset (the program is multi-threaded, just in case
> > you wonder), I get this:
> > 
> > CPU 0+2:  0.0-60.0 sec  4.65 GBytes    665 Mbits/sec
> > CPU 1+3:  0.0-60.0 sec  6.43 GBytes    920 Mbits/sec
> > 
> > That's quite a difference, isn't it?
> > 
> > Now I wonder what CPU 0 is doing...
> 
> Where does /proc/interrupts say the irqs are going?
> 
> 
> 

For me it looks like this:
 24:   52606581          0          0          0   PCI-MSI-edge      eth0

So as I have the same CPU as Michael Riepe, I think CPU0 (core0) servicing
interrupts is related to the issue.

I'm wondering however, if this is expected behavior. iperf and interrupts will
pretty much saturate a core of the atom330. So it looks like a plain CPU bottleneck.

-- 
Greetings, Michael.
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