Re: RFC: [2.6 patch] better i386 CPU selection

Re: RFC: [2.6 patch] better i386 CPU selection

[Mikael Pettersson]

On Sat, 13 Sep 2003 00:51:39 +0200, Adrian Bunk <bunk@fs.tum.de> wrote:
>> > > - Which CPUs exactly need X86_ALIGNMENT_16?
>> >
>> >Unsure. This could use testing on a few systems.
>> 
>> K7s and P5s (and 486s too if I remember correctly) strongly prefer
>> code entry points and loop labels to be 16-byte aligned. This is
>> due to the way code is fetched from L1.
>>...
>
>Hm, that's pretty different from the definition in -test5:
>
>config X86_ALIGNMENT_16
>        bool
>        depends on MWINCHIP3D || MWINCHIP2 || MWINCHIPC6 || MCYRIXIII || 
>          MELAN || MK6 || M586MMX || M586TSC || M586 || M486 || MVIAC3_2
>        default y

My comment referred to data from Intel and AMD code optimisation
guides.

The kernel only uses X86_ALIGNMENT_16 to derive two __ALIGN macros
for assembly code, but it doesn't use them except in one place in
the pnpbios code.

gcc -march=<cpu type> should generate appropriate alignment for
function entries and loop labels.

I suspect X86_ALIGNMENT_16 is a left-over from old code.
Perhaps its time to retire it.

/Mikael

remove __ALIGN from pnpbios/bioscalls.c?

[Adrian Bunk]

On Sat, Sep 13, 2003 at 01:04:32PM +0200, Mikael Pettersson wrote:
> On Sat, 13 Sep 2003 00:51:39 +0200, Adrian Bunk <bunk@fs.tum.de> wrote:
> >> > > - Which CPUs exactly need X86_ALIGNMENT_16?
> >> >
> >> >Unsure. This could use testing on a few systems.
> >> 
> >> K7s and P5s (and 486s too if I remember correctly) strongly prefer
> >> code entry points and loop labels to be 16-byte aligned. This is
> >> due to the way code is fetched from L1.
> >>...
> >
> >Hm, that's pretty different from the definition in -test5:
> >
> >config X86_ALIGNMENT_16
> >        bool
> >        depends on MWINCHIP3D || MWINCHIP2 || MWINCHIPC6 || MCYRIXIII || 
> >          MELAN || MK6 || M586MMX || M586TSC || M586 || M486 || MVIAC3_2
> >        default y
> 
> My comment referred to data from Intel and AMD code optimisation
> guides.
> 
> The kernel only uses X86_ALIGNMENT_16 to derive two __ALIGN macros
> for assembly code, but it doesn't use them except in one place in
> the pnpbios code.

It seems thoe only architecture really using the __ALIGN macros is m68k. 
This is irrelevant in this case since X86_ALIGNMENT_16 only affects 
i386.

> gcc -march=<cpu type> should generate appropriate alignment for
> function entries and loop labels.
> 
> I suspect X86_ALIGNMENT_16 is a left-over from old code.
> Perhaps its time to retire it.

Thomas, what exactly do you need __ALIGN_STR in the function 
pnp_bios_callfunc in drivers/pnp/pnpbios/bioscalls.c for?

> /Mikael

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