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| author |   Bin Gao <bin.gao@linux.intel.com> | 2016-11-15 12:27:21 -0800 |
|---|---|---|
| committer |   Thomas Gleixner <tglx@linutronix.de> | 2016-11-18 10:58:30 +0100 |
| commit | 47c95a46d0fae07762f0a38aa3709ae63f307048 (patch) | |
| tree | 83135dd256323d7d8d8c8108db7353cbe79d452f /arch/x86/kernel/tsc.c | |
| parent | Linux 4.9-rc5 (diff) | |
| download | linux-dev-47c95a46d0fae07762f0a38aa3709ae63f307048.tar.xz linux-dev-47c95a46d0fae07762f0a38aa3709ae63f307048.zip | |
x86/tsc: Add X86_FEATURE_TSC_KNOWN_FREQ flag
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>
Diffstat (limited to 'arch/x86/kernel/tsc.c')
| -rw-r--r-- | arch/x86/kernel/tsc.c | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 46b2f41f8b05..d2c4ee4e4866 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -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; } |