Re: [PATCHSET][2.6-test4][0/6]Support for HPET based timer - Take 2

George Anzinger
2003-09-05T22:21:25Z

Erik Andersen wrote:
> On Fri Aug 29, 2003 at 11:23:47AM -0700, Andrew Morton wrote:
>
>>"Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com> wrote:
>>
>>>Resending the patch.
>>
>>Thanks, I'll include these in the next -mm kernel.
>>
>>Reading the code, the only thing which leaps out is:
>>
>>+/* Use our own asm for 64 bit multiply/divide */
>>+#define ASM_MUL64_REG(eax_out,edx_out,reg_in,eax_in) \
>>+ __asm__ __volatile__("mull %2" \
>>+ :"=a" (eax_out), "=d" (edx_out) \
>>+ :"r" (reg_in), "0" (eax_in))

This can be done in standard C. If you want an inline, how about
(from .../kernel/posix-timers.c):

static inline u64 mpy_l_X_l_ll(unsigned long mpy1,unsigned long mpy2)
{
return (u64)mpy1 * mpy2;
}

>>+
>>+#define ASM_DIV64_REG(eax_out,edx_out,reg_in,eax_in,edx_in) \
>>+ __asm__ __volatile__("divl %2" \
>>+ :"=a" (eax_out), "=d" (edx_out) \
>>+ :"r" (reg_in), "0" (eax_in), "1" (edx_in))

This appears to be the same as (from .../include/asm-i386/div64.h):

#define div_long_long_rem(a,b,c) div_ll_X_l_rem(a,b,c)

extern inline long
div_ll_X_l_rem(long long divs, long div, long *rem)
{
long dum2;
__asm__("divl %2":"=a"(dum2), "=d"(*rem)
: "rm"(div), "A"(divs));

return dum2;

}

-g

>>
>>We seem to keep on proliferating home-grown x86 64-bit math functions.
>>
>>Do you really need these? Is it possible to use do_div() and the C 64x64
>>`*' operator instead?
>
>
>
> The fundamental reason these are proliferating is that given
> some random bit of code such as:
>
> u64 foo=9, bar=3, baz;
> baz = foo / bar;
> baz = foo % bar;
>
> gcc then generates code calling __udivdi3 and __umoddi3. Since
> the kernel does not provide these, people keep reinventing them.
> Perhaps it is time to kill off do_div and all its little friends
> and simply copy __udivdi3 and __umoddi3 from libgcc.....
>
> -Erik
>
> --
> Erik B. Andersen http://codepoet-consulting.com/
> --This message was written using 73% post-consumer electrons--
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--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml