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-rw-r--r--Documentation/kernel-parameters.txt9
-rw-r--r--arch/x86/kernel/tsc.c7
2 files changed, 10 insertions, 6 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 92e83e53148..c7c8eca5b2b 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2467,12 +2467,13 @@ and is between 256 and 4096 characters. It is defined in the file
to facilitate early boot debugging.
See also Documentation/trace/events.txt
- 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.
[x86] noirqtime: Do not use TSC to do irq accounting.
Used to run time disable IRQ_TIME_ACCOUNTING on any
platforms where RDTSC is slow and this accounting
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 0c40d8b7241..bb64beb301d 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -872,6 +872,9 @@ __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:
@@ -879,10 +882,10 @@ __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)