Re: [PATCH] i386-pda UP optimization

[Jeremy Fitzhardinge <jeremy@goop.org>]

Eric Dumazet wrote:
> if !CONFIG_SMP, why even dereferencing boot_pda+PDA_cpu to get 0 ?
> and as PER_CPU(cpu_gdt_descr, %ebx) in !CONFIG_SMP doesnt need the a value in 
> ebx, you can just do :
>
> #define CUR_CPU(reg) /* nothing */
>   

Yep.  On the other hand, I think that's an incredibly rare path anyway,
so it won't make any difference either way.

>> --- a/include/asm-i386/pda.h	Tue Nov 21 18:54:56 2006 -0800
>> +++ b/include/asm-i386/pda.h	Wed Nov 22 02:35:24 2006 -0800
>> @@ -22,6 +22,16 @@ extern struct i386_pda *_cpu_pda[];
>>
>>     
>
> My patch was better IMHO : we dont need to force asm () instructions to 
> perform regular C variable reading/writing in !CONFIG_SMP case.
>
> Using plain C allows compiler to generate a better code.
>   

Probably, but I'm interested in comparing apples with apples; how much
do the actual segment prefixes make a difference?

    J