Bug#721191: linux: patch for parisc/hppa architecture

[Helge Deller <deller@gmx.de>]

On 09/08/2013 04:19 PM, Bastian Blank wrote:
> On Wed, Aug 28, 2013 at 11:53:58PM +0200, Helge Deller wrote:
>> On 08/28/2013 11:35 PM, Bastian Blank wrote:
>>> Looks reasonable. But please send further changes to remove the 
>>> non-smp kernels.
>> I can do that. Do you have some background on this request for me? 
>> Is it policy that you only want to gave SMP-kernels?
> 
> We like to lower the image count.  As long as there are no pressing 
> needs, we like to only have one kernel variant.

Ok.

> Are there any UP machines since PA-8800?

After the request to reduce the kernels to e.g. SMP-only, my thought was
to provide only 32bit-UP and 64bit SMP kernels.
To be sure I asked on the parisc mailing list. The whole thread can be read here:
http://comments.gmane.org/gmane.linux.ports.parisc/5283

Summary:
- yes, there exists quite some 32bit-only parisc SMP machines.
- the J5600 is SMP capable in both 32bit and 64bit mode, but currently it
  only boots Linux with a 32bit SMP kernel and crashes with a 64bit SMP kernel.
  We are working on resolving this...
- 64bit SMP kernel boots fine on a 64bit UP machine. So, theretically we
  can drop the 64bit UP kernel. Only problem: performance loss due to 
  unnecessary spinlock cost. 

So, right now, the best option would be to only drop the 64bit UP kernel.

>>>> PPPS: CONFIG_MLONGCALLS=y is necessary since the built kernel 
>>>> otherwise gets too big so that jumps can't be reached.
>>> Are there drawbacks?
>> Yes, it might be a little bit slower since the jumps now have one 
>> CPU instruction more. But there is no other way to solve it unless 
>> we drop some unneccessary kernel options for parisc.
> 
> How much space would be needed?  Some Arm configs disable SELinux
> for example to save space.

Not much. I think it makes sense to look through the complete configs
again. Maybe there are things which we can disable for parisc...

Helge