SKB corruption on heavy traffic

[Myron.Dixon at L-3com.com]

We have experience a very similar problem using a 2.4.18 kernel on an 8260 ppc processor.
We have a telecomunication product that for some time only used the fec for TCP/IP ethernet 
traffic only and worked just fine.

After we upgraded our product to implement TDM data over IP we started to notice an occasional
kernel oops.  We began to evaluate all of our products and determined that only some of the units
exhibted this behaviour at various rates of occurrence.  Further evaluation revealed that the pointers
located in dpram pointing to the fec's buffer descriptors were some how getting corrupted.
Note that the 8260 has 4 internal scc/fccs and we use all four for various aspects of our application
and each shares dpram for pointers to buffer descriptors that reside in sdram.  However, only the
fec that is used for IP experiences this buffer descriptor corruption and, then, apparently, only under 
heavy traffic load.  We spent about six months evaluating this problem including contacting freescale, 
but never found a solution.  We finally, decided to use an external ethernet chip on a daughter card 
for our IP channel.

It is, however, our belief that our problem relates to a possible bug in the 8260 CPM, but have yet to
absolutely prove this.

If we are experiencing the same problem (and potentially others) and there is a solution we would be
very interested, as, we are not happy about the daughter card solution.  


Myron L. Dixon
Sr. Software Engineer
L-3 Communications, GNS
1519 Grundy's Lane
Bristol, PA 19007
Phone:  215 957 3739
Fax:  215 957 3790
email:  Myron.Dixon at L-3Com.com

-----Original Message-----
From: linuxppc-dev-bounces+myron.dixon=l-3com.com at ozlabs.org [mailto:linuxppc-dev-bounces+myron.dixon=l-3com.com at ozlabs.org] On Behalf Of Franca, Jose (NSN - PT/Portugal - MiniMD)
Sent: Wednesday, April 30, 2008 5:07 AM
To: linuxppc-dev at ozlabs.org; linuxppc-embedded at ozlabs.org
Subject: FW: SKB corruption on heavy traffic

>From our latest debugs we found that the problem occurs mainly on skbuff code. After some variable time kfree or kalloc result in kernel oops.

-----Original Message-----
From: Franca, Jose (NSN - PT/Portugal - MiniMD)
Sent: quarta-feira, 30 de Abril de 2008 9:44
To: 'ext Scott Wood'
Cc: 	
Subject: RE: SKB corruption on heavy traffic

Hello!

	Thank you for replying!
	It't quite dificult to say if the problem exists without our changes, since the all software is dependent on this changes so to work with the hardware. I can't answer to that right now on that, but I forgot to add one thing: we have ring buffer full problems on our fcc_enet driver from time to time. So, I think the problem could be on linux configurations (related to hw) because there is a lot of posts on the web related to problems similar to this (none of them has really solved the bottom problem). 

Regards,
Filipe 

-----Original Message-----
From: ext Scott Wood [mailto:scottwood at freescale.com]
Sent: terça-feira, 29 de Abril de 2008 20:15
To: Franca, Jose (NSN - PT/Portugal - MiniMD)
Cc: linuxppc-dev at ozlabs.org; linuxppc-embedded at ozlabs.org
Subject: Re: SKB corruption on heavy traffic

On Tue, Apr 29, 2008 at 07:39:07PM +0100, Franca, Jose (NSN - PT/Portugal - MiniMD) wrote:
> 	We are developing a MPC8247 based telecom board (512MB), using linux 
> 2.4 with some proprietary changes on IP stack and we are facing some 
> problems when we have heavy traffic on our Ethernet interfaces...

Do you see these problems without the proprietary changes, and with a current kernel?

-Scott
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