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Subject[PATCH] clocksource: Load the ACPI PM clocksource asynchronously
From ef4b0d23878277dfd75828f13353e605aae2937f Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@linux.intel.com>
Date: Mon, 30 Jan 2012 20:23:30 -0800
Subject: [PATCH] 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: Arjan van de Ven <arjan@linux.intel.com>
---
drivers/clocksource/acpi_pm.c | 24 ++++++++++++++++--------
1 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/clocksource/acpi_pm.c b/drivers/clocksource/acpi_pm.c
index 6b5cf02..82e8820 100644
--- a/drivers/clocksource/acpi_pm.c
+++ b/drivers/clocksource/acpi_pm.c
@@ -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
*/
--
1.7.6.4


--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org


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