Messages in this thread Patch in this message | | | Date | Tue, 15 Jun 2004 08:11:09 +0200 | From | Dominik Brodowski <> | Subject | [PATCH 1/3] mull'ify multiplication with HZ in __const_udelay() [Was: Re: Too much error in __const_udelay() ?] |
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John Stultz mentioned on lkml ( http://lkml.org/lkml/2004/6/5/15 ) that calls to udelay() don't delay long enough, causing trouble e.g. in the USB subsystem. The following patches address this issue.
Move the multiplication of (loops_per_jiffy * xloops) with HZ into the "mull" asm operation. This increases the accuracy of the delay functions largely:
n usec delay on a system with loops_per_jiffy = 1500000 :
n before after 1 1000 ticks 1499 ticks 10 14000 ticks 14999 ticks
n usec delay on a system with loops_per_jiffy = 100000 :
n before after 1 0 ticks 99 ticks 10 0 ticks 999 ticks 100 9000 ticks 9999 ticks
As noted by Kurt Garloff, it's necessary to adjust for large loops_per_jiffies, as the multiplication of it with HZ fails for 4GHz or larger. So, John Stultz suggested multiplying xloops with 4 first, and multiplying with (HZ/4).
Signed-off-by: Dominik Brodowski <linux@brodo.de>
diff -ruN linux-original/arch/i386/lib/delay.c linux/arch/i386/lib/delay.c --- linux-original/arch/i386/lib/delay.c 2004-06-14 18:20:27.000000000 +0200 +++ linux/arch/i386/lib/delay.c 2004-06-15 07:48:57.302279400 +0200 @@ -31,10 +31,11 @@ inline void __const_udelay(unsigned long xloops) { int d0; + xloops *= 4; __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/4))); + __delay(xloops); } void __udelay(unsigned long usecs) - 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/
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