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On Mon, 2004-06-07 at 14:20, Dominik Brodowski wrote:
> Move the multiplication of (loops_per_jiffy * xloops) with HZ into
> the "mull" asm operation. This increases the accuracy of the delay functions
> largely:
>
[snip]
> diff -ruN linux-original/arch/i386/lib/delay.c linux/arch/i386/lib/delay.c
> --- linux-original/arch/i386/lib/delay.c 2004-06-07 22:01:46.608351088 +0200
> +++ linux/arch/i386/lib/delay.c 2004-06-07 22:05:03.299449496 +0200
> @@ -33,8 +33,8 @@
> int d0;
> __asm__("mull %0"
> :"=d" (xloops), "=&a" (d0)
> - :"1" (xloops),"0" (current_cpu_data.loops_per_jiffy));
> - __delay(xloops * HZ);
> + :"1" (xloops),"0" (current_cpu_data.loops_per_jiffy * HZ));
> + __delay(xloops);
> }
Kurt Garloff brought up a good point that loops_per_jiffy*HZ is only
good up to 4Ghz time sources. The workaround he suggested was to
multiply xloops by 4 first and divide HZ by 4. This will allow for
frequencies up to 16Ghz.
So something like:
xloops *= 4;
__asm__("mull %0"
:"=d" (xloops), "=&a" (d0)
:"1" (xloops),"0" (LPJ*(HZ/4)));
-john
-
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