Date:	Sat, 7 Jun 2008 12:28:35 -0700
From:	"Ayaz Abdulla" <AAbdulla@...dia.com>
To:	"Karen Shaeffer" <shaeffer@...ralscape.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>, <jgarzik@...ox.com>,
	<manfred@...orfullife.com>, <netdev@...r.kernel.org>
Subject: RE: [PATCH] forcedeth: msi interrupts

Karen,

Is the switch in forced mode? That would explain the mismatch. I can
look into a fix to workaround the hang.

Please open a bugzilla bug as you recommend. Emails get deleted after a
couple of weeks and it is better to have a permanent location to track
issues like this.

Thanks,
Ayaz
 

-----Original Message-----
From: Karen Shaeffer [mailto:shaeffer@...ralscape.com] 
Sent: Saturday, June 07, 2008 11:31 AM
To: Ayaz Abdulla
Cc: Andrew Morton; jgarzik@...ox.com; manfred@...orfullife.com;
netdev@...r.kernel.org
Subject: Re: [PATCH] forcedeth: msi interrupts

On Fri, Jun 06, 2008 at 02:40:16PM -0700, Karen Shaeffer wrote:
> On Fri, Jun 06, 2008 at 02:19:31PM -0700, Ayaz Abdulla wrote:
> > Yes, that would be great!
> 
> Hi Ayaz,
> How far back should it be back ported? Do you know?


Hello,
Let me explain and maybe get some advice. I have recently done work with
the Sun Netra X4200 M2 Server that uses the Nvidia CK48 chipset and the
forcedeth driver. You can see an architecture overview here:
http://www.sun.com/servers/netra/x4200/wp.pdf

The Nvidia NIC that is integrated into the Nvidia 2200 chip, has a
failure mode for the following linux kernels 2.6.21.x 2.6.23.x 2.6.24.x
RHEL 2.6.18*

The NIC will hang under specific conditions for all these kernels.
First, you must run the NIC in 100 Mb mode with autoneg enabled, then it
will always link in a mismatch with the switch.
The switch will link at 100 Mb full duplex, while the Nvidia NIC will
link at 100 Mb half duplex. This was shown with both Cisco managed
switches and HP managed switches, and I suspect it will happen with any
switch. (You can force the NIC to 100 Mb full, but autoneg will always
result in the link mismatch.)

Once this link mismatch is in effect, then, if you run it long enough,
the NIC will eventually hang and become completely disabled. (I know you
shouldn't run a NIC in link mismatch, but end users in the field
sometimes don't realize it has happened.) It could take days or weeks
under reasonably heavy load, but it will always hang in the end.
Continually rebooting the server will result in the hang in a matter of
hours, where the link negotiation results in the hang. No packets are
ever transmitted in these cases. Because it is reproducable in a matter
of hours, this is the preferred way to reproduce the failure mode.

The ethtool online test will pass. The ethtool offline test will fail.
The driver does TX register dumps into the logs and reports TX busy
errors. I provided all this information to Ayaz in real time, but never
got any response or comment from him.

Even a soft reboot will not clear this failure. This initially lead me
to conclude this is a hardware failure, but it isn't 100% certain to be
the case. This is because the NIC is known to hang at boot time during
the link negotiation, where no packets are ever transmitted. I didn't
have time to fully understand this failure mode, but it could be that a
soft reboot does clear the failure. And then at boot time link
negotiation, it fails immediately, giving the appearance of a HW failure
sustained across a soft reboot. I did not investigate enough to conclude
with certainty it is a HW failure.

I did determine that a double hard reboot, where the second reboot is
executed while the Netra is in the BIOS POST will always clear the NIC
failure. This lead me to conclude with reasonable certainty this is a
hardware failure that can occur at 100 Mb mode with a link mismatch. But
I am not certain as stated above. Nvidia never did provide a resolution
to this problem, despite the fact they were provided substantial
information characterizing the failures and clear instructions on how to
reproduce it within a few hours.

I've always known there may be a driver workaround for this failure. And
if there is a driver workaround it would likely be related to
interrupts. So, that was my motivation to ask the original question
here. In the future, I will likely just dump all the data into bugzilla,
as it seems like the preferred response to such a set of circumtances.

Thanks,
Karen

> > -----Original Message-----
> > From: Andrew Morton [mailto:akpm@...ux-foundation.org]
> > Sent: Friday, June 06, 2008 2:11 PM
> > To: Ayaz Abdulla
> > Cc: jgarzik@...ox.com; manfred@...orfullife.com; 
> > netdev@...r.kernel.org
> > Subject: Re: [PATCH] forcedeth: msi interrupts
> > 
> > 
> > On Fri, 06 Jun 2008 14:04:05 -0400
> > Ayaz Abdulla <aabdulla@...dia.com> wrote:
> > 
> > > 
> > > 
> > > Andrew Morton wrote:
> > > > On Fri, 06 Jun 2008 13:15:32 -0400 Ayaz Abdulla 
> > > > <aabdulla@...dia.com> wrote:
> > > > 
> > > > 
> > > >>Andrew Morton wrote:
> > > >>
> > > >>>On Tue, 03 Jun 2008 16:51:46 -0400 Ayaz Abdulla 
> > > >>><aabdulla@...dia.com> wrote:
> > > >>>
> > > >>> > This patch adds a workaround for lost MSI interrupts. There 
> > > >>> > is a
> > race
> > > >>> > condition in the HW in which future interrupts could be
missed.
> > The
> > > >>> > workaround is to toggle the MSI irq mask.
> > > >>> >
> > > >>>
> > > >>>Do you think this is a 2.6.26 thing?
> > > >>
> > > >>It is by HW design, not related to the kernel.
> > > > 
> > > > 
> > > > Sorry, what I meant was: do you believe that this patch should 
> > > > be in 2.6.26?
> > > Yes, it should be treated as a critical fix.
> > 
> > So should it also be backported into 2.6.25.x?
> > 
> > Bear in mind that $major_distros are apparently basing product on 
> > 2.6.25.
--
 Karen Shaeffer
 Neuralscape, Palo Alto, Ca. 94306
 shaeffer@...ralscape.com  http://www.neuralscape.com
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