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x86/tsc: Add X86_FEATURE_TSC_KNOWN_FREQ flag

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The X86_FEATURE_TSC_RELIABLE flag in Linux kernel implies both reliable
(at runtime) and trustable (at calibration). But reliable running and
trustable calibration independent of each other. 

Add a new flag X86_FEATURE_TSC_KNOWN_FREQ, which denotes that the frequency
is known (via MSR/CPUID). This flag is only meant to skip the long term
calibration on systems which have a known frequency.

Add X86_FEATURE_TSC_KNOWN_FREQ to the skip the delayed calibration and
leave X86_FEATURE_TSC_RELIABLE in place.

After converting the existing users of X86_FEATURE_TSC_RELIABLE to use
either both flags or just X86_FEATURE_TSC_KNOWN_FREQ we can seperate the
functionality.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Bin Gao <bin.gao@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1479241644-234277-2-git-send-email-bin.gao@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Bin Gao
2016-11-15 12:27:21 -08:00
committed by Thomas Gleixner
parent a25f0944ba
commit 47c95a46d0
2 changed files with 9 additions and 3 deletions
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11
arch/x86/kernel/tsc.c
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@@ -1283,10 +1283,15 @@ static int __init init_tsc_clocksource(void)
clocksource_tsc.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP;
/*
* Trust the results of the earlier calibration on systems
* exporting a reliable TSC.
* When TSC frequency is known (retrieved via MSR or CPUID), we skip
* the refined calibration and directly register it as a clocksource.
*
* We still keep the TSC_RELIABLE flag here to avoid regressions -
* it will be removed after all the conversion for other code paths
* connected to this flag is done.
*/
if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE) ||
boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) {
clocksource_register_khz(&clocksource_tsc, tsc_khz);
return 0;
}