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clocksource: Load the ACPI PM clocksource asynchronously

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The ACPI clocksource takes quite some time to initialize,
and this increases the boot time of the kernel for a
double digit percentage. This while almost all modern
systems will be using the HPET already anyway.

This patch turns the clocksource loading into an asynchronous
operation; which means it won't hold up the boot while
still becoming available normally.

To make this work well, an udelay() had to be turned into an
usleep_range() so that on UP systems, we yield the CPU to
regular boot tasks instead of spinning.

CC: John Stultz <johnstul@us.ibm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Len Brown <lenb@kernel.org>

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
This commit is contained in:
Arjan van de Ven 2012-01-30 20:23:30 -08:00 committed by John Stultz
parent 12d6d41276
commit b519508298
1 changed files with 16 additions and 8 deletions
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24
drivers/clocksource/acpi_pm.c
View file

@ -23,6 +23,7 @@
#include <linux/init.h>
#include <linux/pci.h>
#include <linux/delay.h>
#include <linux/async.h>
#include <asm/io.h>
/*
@ -179,17 +180,15 @@ static int verify_pmtmr_rate(void)
/* Number of reads we try to get two different values */
#define ACPI_PM_READ_CHECKS 10000
static int __init init_acpi_pm_clocksource(void)
static void __init acpi_pm_clocksource_async(void *unused, async_cookie_t cookie)
{
cycle_t value1, value2;
unsigned int i, j = 0;
if (!pmtmr_ioport)
return -ENODEV;
/* "verify" this timing source: */
for (j = 0; j < ACPI_PM_MONOTONICITY_CHECKS; j++) {
udelay(100 * j);
usleep_range(100 * j, 100 * j + 100);
value1 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
for (i = 0; i < ACPI_PM_READ_CHECKS; i++) {
value2 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
@ -203,25 +202,34 @@ static int __init init_acpi_pm_clocksource(void)
" 0x%#llx, 0x%#llx - aborting.\n",
value1, value2);
pmtmr_ioport = 0;
return -EINVAL;
return;
}
if (i == ACPI_PM_READ_CHECKS) {
printk(KERN_INFO "PM-Timer failed consistency check "
" (0x%#llx) - aborting.\n", value1);
pmtmr_ioport = 0;
return -ENODEV;
return;
}
}
if (verify_pmtmr_rate() != 0){
pmtmr_ioport = 0;
return -ENODEV;
return;
}
return clocksource_register_hz(&clocksource_acpi_pm,
clocksource_register_hz(&clocksource_acpi_pm,
PMTMR_TICKS_PER_SEC);
}
static int __init init_acpi_pm_clocksource(void)
{
if (!pmtmr_ioport)
return -ENODEV;
async_schedule(acpi_pm_clocksource_async, NULL);
return 0;
}
/* We use fs_initcall because we want the PCI fixups to have run
* but we still need to load before device_initcall
*/