Subject: Re: NFS problems on a MPC5200-based board

From: Benjamin Herrenschmidt <[email-masked]>
Date: Thu, 12 Mar 2009 08:39:26 +1100

On Wed, 2009-03-11 at 16:08 +0100, Bartłomiej Sięka wrote:
> Hi,
> 
> This is a follow-up on NFS problems on an MPC5200-based board reported  
> here a while back:
> 
> http://www.nabble.com/-PATCH--Add-support-for-the-digsy-MTC-board.-to21750004.html#a21792612
> 
> To recap: while using NFS, especially while mounting the root  
> filesystem over NFS, the system is really slow and displays a bunch of  
> "nfs: server 192.168.1.1 not responding, still trying" messages.  
> Sometimes it is able to get to the login prompt, sometimes not. In  
> cases where the login is successful, the system is still extremely  
> sluggish (console hangs for tens of seconds and longer).
> 
> git bisect narrows down the troublesome commit as:

Maybe you need to set CPU_FTR_NEED_COHERENT for the 5200 ?

Cheers,
Ben.

> commit 4c456a67f501b8b15542c7c21c28812bf88f484b
> Author: Gerhard Pircher <[email-masked]>
> Date:   Fri Jan 23 06:51:28 2009 +0000
> 
>     powerpc/mm: Fix handling of _PAGE_COHERENT in BAT setup code
> 
>     _PAGE_COHERENT is now always set in _PAGE_RAM resp. PAGE_KERNEL.
>     Thus it has to be masked out, if the BAT mapping should be non
>     cacheable or CPU_FTR_NEED_COHERENT is not set.
> 
>     This will work on normal SMP setups because we force-set
>     CPU_FTR_NEED_COHERENT as part of CPU_FTR_COMMON on SMP.
> 
>     Signed-off-by: Gerhard Pircher <[email-masked]>
>     Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
> 
> 
> We have tested recent mainline kernel (past 2.6.29-rc7) with the  
> 4c456a6...
> commit reverted and NFS problems went away.
> 
> Other people have also reported similar problems (original posters on  
> Cc):
> http://www.nabble.com/-PATCH--Add-support-for-the-digsy-MTC-board.-tp21750004p21792825.html
> http://www.nabble.com/-PATCH--Add-support-for-the-digsy-MTC-board.-tp21750004p21792612.html
> 
> The commit in question does not look directly related to NFS/ 
> networking; moreover it is a fix for some other problem, so just  
> reverting it is not an option, it seems (?). So how do we go about  
> having NFS operational again? Any comments?
> 
> Regards,
> Bartlomiej Sieka