lkml.org 
[lkml]   [2007]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] [7/30] x86_64: Avoid overflows during apic timer calibration
Date

From: David P. Reed <dpreed@reed.com>

- Use 64bit TSC calculations to avoid handling overflow
- Use 32bit unsigned arithmetic for the APIC timer. This
way overflows are handled correctly.
- Fix exit check of loop to account for apic timer counting down

Signed-off-by: dpreed@reed.com
Signed-off-by: Andi Kleen <ak@suse.de>

---
arch/x86_64/kernel/apic.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
Index: linux/arch/x86_64/kernel/apic.c
===================================================================
--- linux.orig/arch/x86_64/kernel/apic.c
+++ linux/arch/x86_64/kernel/apic.c
@@ -839,14 +839,15 @@ static void setup_APIC_timer(unsigned in

static int __init calibrate_APIC_clock(void)
{
- int apic, apic_start, tsc, tsc_start;
+ unsigned apic, apic_start;
+ unsigned long tsc, tsc_start;
int result;
/*
* Put whatever arbitrary (but long enough) timeout
* value into the APIC clock, we just want to get the
* counter running for calibration.
*/
- __setup_APIC_LVTT(1000000000);
+ __setup_APIC_LVTT(4000000000);

apic_start = apic_read(APIC_TMCCT);
#ifdef CONFIG_X86_PM_TIMER
@@ -857,13 +858,13 @@ static int __init calibrate_APIC_clock(v
} else
#endif
{
- rdtscl(tsc_start);
+ rdtscll(tsc_start);

do {
apic = apic_read(APIC_TMCCT);
- rdtscl(tsc);
+ rdtscll(tsc);
} while ((tsc - tsc_start) < TICK_COUNT &&
- (apic - apic_start) < TICK_COUNT);
+ (apic_start - apic) < TICK_COUNT);

result = (apic_start - apic) * 1000L * tsc_khz /
(tsc - tsc_start);
-
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: 2007-05-01 06:07    [from the cache]
©2003-2011 Jasper Spaans