Re: [1/4] better i386 CPU selection

[Adrian Bunk <bunk@fs.tum.de>]

On Sat, Jan 17, 2004 at 10:13:37AM +0100, Robert Schwebel wrote:

> Hi, 

Hi Robert,

> On Sat, Jan 17, 2004 at 03:15:32AM +0100, Adrian Bunk wrote:
> > Besides the AMD Elan cpufreq driver I see nothing where CONFIG_MELAN
> > gave you any real difference (except your highest goal is to avoid a
> > recompilation when switching from the Pentium 4 to the AMD Elan - but I
> > doubt the really "prevents development").
> > 
> > But I'm not religious about this issue. Let Robert decide, the Elan 
> > support is his child.
> > 
> > > > > - added optimizing CFLAGS for the AMD Elan
> > > 
> > > There are no such different "optimizations" for ELAN.
> > 
> > What's wrong wih the -march=i486 Robert suggested?
> 
> I've not followed the 2.6 development regarding the arch selection that
> closely; let's collect arguments: 
> 
> - Is it still possible to run a -march=i486 built kernel on a pentium? 
>   IMHO It would be good to optimize the code for i486, but I'm not that 
>   familiar with how good gcc optimizes for 486 that I can comment this.

yes, since a Pentium supports a superset of the 486 gcc can't optimize 
for a 486 in a way that the code won't run on a Pentium.

> - I personally work with lots of cross architectures like ARM, so cross
>   compiling for an embedded system is no problem for me. But if people
>   want to test stuff on their pentiums I also have no problem with that.
> 
> Other arguments? 

The only reason why I sent the patch to make the AMD Elan a separate 
subarch was the CLOCK_TICK_RATE #ifdef in include/asm-i386/timex.h .

It should be possible to change it to a variable (as with 
CONFIG_X86_PC9800) if both the Elan and a different cpu are supported if 
this is really a required use.

If this is the solution you prefer, how would you do runtime detection 
for the AMD Elan?

> Robert

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed