Message-ID: <201201241152.21472.tim.sander@hbm.com>
Date:	Tue, 24 Jan 2012 11:52:21 +0100
From:	"Tim Sander" <tim.sander@....com>
To:	"RT" <linux-rt-users@...r.kernel.org>
Cc:	"Mike Galbraith" <efault@....de>,
	"Tim Sander" <tstone@....tu-darmstadt.de>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Clark Williams" <williams@...hat.com>,
	"John Kacur" <jkacur@...hat.com>,
	"Gerlando Falauto" <gerlando.falauto@...mile.com>,
	"Micha Nelissen" <micha@...i.hopto.org>,
	"Holger Brunck" <holger.brunck@...mile.com>
Subject: Re: [ANNOUNCE] 3.0.14-rt31 - ksoftirq running wild - FEC ethernet driver to blame? Yep

Hi 

I have some more info on the error report, please see below.
> Well thanks for your patch. It didn't apply cleanly due to some moved
> lines, but nothing to serious. I now have a machine where top just shows
> me the culprit:
> sirq-net-tx/0
> 
> It seems to be triggered not as often as the mainline rt kernel though. But
> after some starts and stops of "connmand" and "ifconfig eth0 down" i got
> back this errornous behaviour. The only question is what next? Still i
> have some more observations which might help to nail down this bug:
> * ifconfig does not return when sirq-net-tx/0 eats all cpu
> * sometimes sirq-net-tx/0 sits on the cpu for a couple of seconds and goes
> away, somtimes it just stays there when "ifconfig eth0 up" is issued.
> * There are suspicious "FEC: MDIO read timeout" kernel log messages from
> the ethernet driver.
> * The ethernet phy uses polling since i do not know how to set the phy irq
> in the board definition. I tried using "phy_register_fixup_for_uid" and
> then setting the phy_dev->irq int the fixup routine but that seems to be
> to late and the interrupt is deregisterd but has not been registered when
> the network device is shut down.
> I also didn't found a example in the source and there has been no word in
> the phy.txt documentation about it? So input on how to set the phy irq in
> the board config of the pcm043 would be really nice.
> 
I would like to point out that the running wild softirq seems to bee fixed by
9ec14c04ec6be93ff397adf250bc91ee77742bfb of the stable git tree.
At least i could not reproduce the ksoftirq error with 3.0.17-rt33. With the 
above commit reverted i could reproduce this error. As this running wild 
ksoftirq did not occur regularly there is a small chance that this error just 
didn't show up with the new kernel but i doubt it.

There is still the case that on network configuration the systemload with 
ksoftirq goes suspicoiusly high but at least it gets to normal levels 
afterwards. 

Best regards
Tim

PS: I have added the cc list of that commit to this report. If you guys have  
some insight on this you could share that would be great.

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