Re: do_div64 generic

george anzinger
2003-07-15T21:38:58Z

Bernardo Innocenti wrote:
> On Tuesday 15 July 2003 07:38, Andrew Morton wrote:
>
>
>>> Here's a patch that takes care of all architectures.
>>
>>AFAICT, we can just rework posix-timers.c to use the standard do_div() and
>>be done with it, can we not? ie: no div_long_long_rem(), no
>>div_ll_X_l_rem(). Just do_div().
>
>
> We could, and it would be easy and almost as efficient in all places
> where div_long_long_rem() is being used:
>
> value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec);
>
> becomes:
>
> value->tv_nsec = do_div(nsec, NSEC_PER_SEC);
> value->tv_sec = nsec;
>
> George, do you agree? May I go on and post a patch killing
> div_long_long_rem() everywhere?

The issue is that div is a very long instruction and the do_div()
thing uses 2 or three of them, while the div_long_long_rem() is just
1. Also, a lot of archs already have the required div by a different
name. It all boils down to a performance thing.

-g
>
>
>>Please use `static inline', not `extern inline', btw.
>
>
> Oops. Fixed. I had just copied it over from asm-i386/div64.h.
>
> Is it worth posting a big patch to replace all remaining
> occurrences of 'extern inline' all over the kernel?
>
> I'd also like to point out that __inline__ is often being
> used inconsistently. We should be using __inline__ rather
> than inline in public headers needed by glibc for apps
> compiled with -ansi. Since it's so ugly, it shouldn't
> be used in other places.
>

--
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