linux-kernel - [PATCH] [7/30] x86_64: Avoid overflows during apic timer calibration

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Date:	Tue,  1 May 2007 05:58:04 +0200 (CEST)
From:	Andi Kleen <ak@...e.de>
To:	dpreed@...d.com, patches@...-64.org, linux-kernel@...r.kernel.org
Subject: [PATCH] [7/30] x86_64: Avoid overflows during apic timer calibration


From: David P. Reed <dpreed@...d.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@...d.com
Signed-off-by: Andi Kleen <ak@...e.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);
-
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