Messages in this thread | | | Subject | Re: [PATCH 1/3] mull'ify multiplication with HZ in __const_udelay() [Was: Re: Too much error in __const_udelay() ?] | From | john stultz <> | Date | Mon, 07 Jun 2004 15:00:56 -0700 |
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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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