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x86/tsc: Enumerate SKL cpu_khz and tsc_khz via CPUID

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Skylake CPU base-frequency and TSC frequency may differ
by up to 2%.

Enumerate CPU and TSC frequencies separately, allowing
cpu_khz and tsc_khz to differ.

The existing CPU frequency calibration mechanism is unchanged.
However, CPUID extensions are preferred, when available.

CPUID.0x16 is preferred over MSR and timer calibration
for CPU frequency discovery.

CPUID.0x15 takes precedence over CPU-frequency
for TSC frequency discovery.

Signed-off-by: Len Brown <len.brown@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/b27ec289fd005833b27d694d9c2dbb716c5cdff7.1466138954.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Len Brown
2016-06-17 01:22:51 -04:00
committed by Ingo Molnar
parent 02c0cd2dcf
commit aa297292d7
4 changed files with 73 additions and 8 deletions
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arch/x86/include/asm/tsc.h
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@@ -36,6 +36,7 @@ extern void mark_tsc_unstable(char *reason);
extern int unsynchronized_tsc(void);
extern int check_tsc_unstable(void);
extern int check_tsc_disabled(void);
extern unsigned long native_calibrate_cpu(void);
extern unsigned long native_calibrate_tsc(void);
extern unsigned long long native_sched_clock_from_tsc(u64 tsc);