lkml.org 
[lkml]   [2004]   [Jun]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/3] mull'ify multiplication with HZ in __const_udelay() [Was: Re: Too much error in __const_udelay() ?]
From
Date
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

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:03    [W:0.046 / U:1.092 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site