Re: [RFC][PATCH] tsc_khz= boot option to avoid TSC calibration variance

[George Spelvin]

> I'd suggest the following:

I should add the documentation patch that goes with it:
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 90b3924..6747881 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2391,10 +2391,20 @@ and is between 256 and 4096 characters. It is defined in the file
 
 	tsc=		Disable clocksource-must-verify flag 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.
+			[x86] if value is "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.
+
+	tsc_khz=	[x86] Set the TSC freq value.
+			Format: <khz>
+			Used to avoid TSC calibration error.  The TSC frequency
+			is re-measured each boot, and changes by a few parts
+			per hundred thousand each time.  This is noticeable to
+			time synchronization applications like NTP.
+			This option makes it consistent across boots.
+			If the specified value differs from the measured one
+			by more than 0.1%, it is ignored.
 
 	turbografx.map[2|3]=	[HW,JOY]
 			TurboGraFX parallel port interface
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