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x86: Make tsc=reliable override boot time stability checks 

This patch makes the tsc=reliable option disable the boot time
stability checks. Currently the option only disables the runtime
watchdog checks. This change allows folks who want to override the
boot time TSC stability checks and use the TSC when the system would
otherwise disqualify it.

There still are some situations that the TSC will be disqualified,
such as cpufreq scaling. But these are situations where the box will
hang if allowed.

Patch also includes a fix for an issue found by Thomas Gleixner, where
the TSC disqualification message wouldn't be printed after a call to
unsynchronized_tsc().

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: akataria@vmware.com
Cc: Stephen Hemminger <shemminger@vyatta.com>
LKML-Reference: <1250552447.7212.92.camel@localhost.localdomain>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
john stultz 2009-08-17 16:40:47 -07:00 committed by Thomas Gleixner
parent 326ba5010a
commit d3b8f889a2
2 changed files with 10 additions and 6 deletions
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9
Documentation/kernel-parameters.txt
View File

@ -2484,12 +2484,13 @@ and is between 256 and 4096 characters. It is defined in the file
Format:
<io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
tsc= Disable clocksource-must-verify flag for TSC.
tsc= Disable clocksource stability checks for TSC.
Format: <string>
[x86] reliable: mark tsc clocksource as reliable, this
disables clocksource verification at runtime.
Used to enable high-resolution timer mode on older
hardware, and in virtualized environment.
disables clocksource verification at runtime, as well
as the stability checks done at bootup. Used to enable
high-resolution timer mode on older hardware, and in
virtualized environment.
turbografx.map[2|3]= [HW,JOY]
TurboGraFX parallel port interface

7
arch/x86/kernel/tsc.c
View File

@ -825,6 +825,9 @@ __cpuinit int unsynchronized_tsc(void)
if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
return 0;
if (tsc_clocksource_reliable)
return 0;
/*
* Intel systems are normally all synchronized.
* Exceptions must mark TSC as unstable:
@ -832,10 +835,10 @@ __cpuinit int unsynchronized_tsc(void)
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
/* assume multi socket systems are not synchronized: */
if (num_possible_cpus() > 1)
tsc_unstable = 1;
return 1;
}
return tsc_unstable;
return 0;
}
static void __init init_tsc_clocksource(void)