lubuntu-desktop team mailing list archive

[Yorvyk <yorvik.ubunto@xxxxxxxxxxxxxx>]

On Sun, 20 Nov 2011 13:20:35 -0800
Jonathan Marsden <jmarsden@xxxxxxxxxxx> wrote:

> On 11/20/2011 07:29 AM, Chow Loong Jin wrote:
> 
> > On 20/11/2011 19:31, Yorvyk wrote:
> 
> 
> >> If a CPU can't support PAE it can't support more than 4GiB of RAM,
> >> so the PAE part of the kernel shoudn't come into play.
> 
>  
> 
> > From what I understand, PAE has a different set of paging structures
> > compared to non-PAE. Does the kernel know to fall back onto non-PAE
> > mode if it cannot enable PAE on a CPU?
> 
> 
> Which way to do things is basically a compile time option for the
> kernel, as I understand it.  So, if a PAE kernel is used, it can *only*
> be run on processors that support the additional PAE instructions.  Even
> if a machine only has 128MB RAM, it you try to run a PAE kernel on it,
> and the CPU lacks the PAE instruction, it is not going to run.
> 
> The real question is: are there really any CPUs in general purpose
> desktops or laptops, in any significant quantity at all, that Ubuntu
> 11.10 i386 kernels work on, which PAE kernels do not work on?
> 
> Other than the early 400MHz Pentium-M, which are pretty rare, I don't
> think anyone has seen such a CPU yet.  Via C3 and AMD Geode LX already
> cannot run current Ubuntu 11.10 default kernels anyway.
> 
Having trawled the net for info on this, I have no problem with dropping the non-PAE kernel as it appears to only effect a very,very, very small number of users.  Whether these are current or potential users is going to be very hard to find out, unless they start jumping up-and-down screaming.
My one concern was the alleged overhead of the PAE kernel but, this appears, from the various benchmarks I've seen, to be trivial and probably unnoticeable in normal use.  I have installed PAE kernels on a couple of machines, one oneiric and one precise, and have not noticed any problems so far.
I would imagine by the time 12.04 is no longer supported, 32 bit ubuntus may well be limited to the ARM anyway.




-- 
Yorvyk