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Old 01-27-2009, 02:37 PM
Stefan Bader
 
Default LP#74179 -- support for i386 machines with >3GB RAM

Scott James Remnant wrote:
> On Tue, 2009-01-27 at 13:51 +0000, Andy Whitcroft wrote:
>
>> Therefore I am proposing we create a new i386 only flavour generic64g
>> which is identicle to the generic flavour except that it enables PAE and
>> options that that requires.
>>
> What are the downsides of just enabling PAE in the generic kernel?

The downside is that CPUs without PAE support do not boot. And that are still
some around.

Stefan

>
> Scott
>


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Old 01-27-2009, 03:48 PM
Tim Gardner
 
Default LP#74179 -- support for i386 machines with >3GB RAM

Scott James Remnant wrote:
> On Tue, 2009-01-27 at 16:37 +0100, Stefan Bader wrote:
>
>> Scott James Remnant wrote:
>>> On Tue, 2009-01-27 at 13:51 +0000, Andy Whitcroft wrote:
>>>
>>>> Therefore I am proposing we create a new i386 only flavour generic64g
>>>> which is identicle to the generic flavour except that it enables PAE and
>>>> options that that requires.
>>>>
>>> What are the downsides of just enabling PAE in the generic kernel?
>> The downside is that CPUs without PAE support do not boot. And that are still
>> some around.
>>
> Which CPUs, specifically?
>
> Do they not boot, or just not address areas of memory?
>
> Is there no way for the kernel to detect this like it does with just
> about every other CPU feature and disable it on the fly?
>
> Scott
>

There are a whole class of VIA cpus that do not support PAE. They are
popular in some low powered gateways.

rtg
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Old 01-27-2009, 07:46 PM
Tim Gardner
 
Default LP#74179 -- support for i386 machines with >3GB RAM

Andy Whitcroft wrote:
> On Tue, Jan 27, 2009 at 07:38:46AM -0700, Tim Gardner wrote:
>
>> I am not in favor of another flavor. Despite the reluctance of some
>> folks to use the server flavour, it _does_ solve their use case with no
>> effort on our part. If these users are that sensitive to the
>> optimization differences between generic and server, then they'll have
>> to run a 64 bit kernel.
>>
>> My goal is to actually reduce the i386 flavours for Jaunty+1 to just
>> generic. Hardy should be the last LTS that supports a 32 bit server.
>
> Then if we plan on having just one flavour in N+1 that would have to be
> PAE enabled.
>

Quite the opposite IMHO. The only flavour left in i386 would be non-PAE
in order to support those 32 bit CPUs that do not have PAE. While there
are still 32 bit CPUs with PAE support, they are becoming old enough
that I'm no longer interested in supporting them. The number of those
that have more then 4Gb is even fewer.

> I thought the issue there was that some older h/w doesn't support PAE
> necessarily (i want to say lpia is in this situation though am not sure
> why) so we would end up needing an PAE and non-PAE build still?
>

LPIA is a completely separate arch from i386, so the PAE issues aren't
relevant. We'll do what is needed to satisfy the mobile team.

Remember, I'm trying balance the use cases against maintenance and build
overhead. I'm open to opinions, but I think many of these use cases are
falling below the cut line.

rtg
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