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clocksource, acpi_pm.c: check for monotonicity

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The current check for monotonicity is way too weak: Andreas Mohr reports (
http://lkml.org/lkml/2008/8/10/77 ) that on one of his test systems the
current check only triggers in 50% of all cases, leading to catastrophic
timer behaviour.  To fix this issue, expand the check for monotonicity by
doing ten consecutive tests instead of one.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Dominik Brodowski 2008-09-05 14:05:35 -07:00 committed by Ingo Molnar
parent dfdf748a61
commit 4ab6a21911
1 changed files with 29 additions and 17 deletions
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46
drivers/clocksource/acpi_pm.c
View file

@ -21,6 +21,7 @@
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/pci.h>
#include <linux/delay.h>
#include <asm/io.h>
/*
@ -175,10 +176,13 @@ static int verify_pmtmr_rate(void)
#define verify_pmtmr_rate() (0)
#endif
/* Number of monotonicity checks to perform during initialization */
#define ACPI_PM_MONOTONICITY_CHECKS 10
static int __init init_acpi_pm_clocksource(void)
{
cycle_t value1, value2;
unsigned int i;
unsigned int i, j, good = 0;
if (!pmtmr_ioport)
return -ENODEV;
@ -187,24 +191,32 @@ static int __init init_acpi_pm_clocksource(void)
clocksource_acpi_pm.shift);
/* "verify" this timing source: */
value1 = clocksource_acpi_pm.read();
for (i = 0; i < 10000; i++) {
value2 = clocksource_acpi_pm.read();
if (value2 == value1)
continue;
if (value2 > value1)
goto pm_good;
if ((value2 < value1) && ((value2) < 0xFFF))
goto pm_good;
printk(KERN_INFO "PM-Timer had inconsistent results:"
" 0x%#llx, 0x%#llx - aborting.\n", value1, value2);
return -EINVAL;
for (j = 0; j < ACPI_PM_MONOTONICITY_CHECKS; j++) {
value1 = clocksource_acpi_pm.read();
for (i = 0; i < 10000; i++) {
value2 = clocksource_acpi_pm.read();
if (value2 == value1)
continue;
if (value2 > value1)
good++;
break;
if ((value2 < value1) && ((value2) < 0xFFF))
good++;
break;
printk(KERN_INFO "PM-Timer had inconsistent results:"
" 0x%#llx, 0x%#llx - aborting.\n",
value1, value2);
return -EINVAL;
}
udelay(300 * i);
}
if (good != ACPI_PM_MONOTONICITY_CHECKS) {
printk(KERN_INFO "PM-Timer failed consistency check "
" (0x%#llx) - aborting.\n", value1);
return -ENODEV;
}
printk(KERN_INFO "PM-Timer had no reasonable result:"
" 0x%#llx - aborting.\n", value1);
return -ENODEV;
pm_good:
if (verify_pmtmr_rate() != 0)
return -ENODEV;