[Cbe-oss-dev] Only 86MB of RAM available running Ubuntu 8.04 powerpc64-smp kernel on PS3

[Geoff Levand]

Dan Munckton wrote:
> Hi Geoff
> 
>> Yes, all firmware versions to date give 128 MiB of boot memory.
>> 
>> The VMEMMAP authors didn't consider systems that don't have much
>> memory when they did there design, so it doesn't really work well
>> on PS3.  With your config it needs a 16MiB page of boot memory to
>> add the extra hot plug memory.  The above message shows that this
>> alloc failed, so the hot plug mem could not be added.  The system
>> then continues to boot with just the 128 MiB of boot mem.
>> 
>> Looking at the .config here:
>> 
>>   http://launchpadlibrarian.net/13914707/config-2.6.24-16-powerpc64-smp
>> 
>> The trouble is that CONFIG_SPARSEMEM_VMEMMAP is set, and the kernel
>> image is very big do to all the other options set.
>> 
>> You have two choices for your Hardy support.  The easier way, and
>> better for PS3 users, is to make a ps3 specific kernel, the harder
>> way is to tune the multi-platform kernel so that it boots on the PS3.
>> 
>> Either way, change to these:
>> 
>>   CONFIG_SPARSEMEM_VMEMMAP=n
>>   CONFIG_FB_PS3_DEFAULT_SIZE_M=9
>>   CONFIG_PS3_USE_LPAR_ADDR=n
>> 
>> -Geoff
>> 
> 
> Interesting. Thanks for the explanation. I note that SPARSEMEM_VMEMMAP
> and PS3_USE_LPAR_ADDR are both set to 'y' even in the
> ps3_defconfig .config, so you're suggesting these options cannot be used
> in such a big kernel until something like Ben's patch absorbed into the
> vmemmap code. 
> 
> Are there likely to be any noticeable side-effects of losing these two
> features?


CONFIG_PS3_USE_LPAR_ADDR was needed to work around a hack in the spu
support which is fixed in later kernels.  Check if your kernel uses 
SPARSEMEM for its spu support, or test if spufs doesn't work with
CONFIG_PS3_USE_LPAR_ADDR=n.

With CONFIG_SPARSEMEM_VMEMMAP=n the kernel will use more memory on
machines with lots of memory.


> I also noticed the FB is getting allocated an extra 9MB of space in the
> hardy config. Obviously we can get by with only 9MB, so I presume the
> motivation for 16MB would better support double-buffering/flipping is
> that correct? What side effects would be incurred by setting this to
> 9MB?

The system won't support flipping for hi-res modes.  Flipping is a
rarely used feature.

> I am probably going to propose to the Ubuntu Kernel Team that the PS3
> kernel is supported as a "custom flavour" build again as it was in
> gutsy/feisty. Do you think that an attempt to use the generic
> powerpc64-smp flavour would be worth trying again with 2.6.2{5,6}?

It can be done either way.

-Geoff