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Commit b5195082 authored by Arjan van de Ven's avatar Arjan van de Ven Committed by John Stultz
Browse files

clocksource: Load the ACPI PM clocksource asynchronously 



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: default avatarArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
parent 12d6d412

drivers/clocksource/acpi_pm.c

+16 −8
Original line number Diff line number Diff line
@@ -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

 */