Commit-ID: 4ca4df0b7eb06df264b2919759957f6d6ea1822e Gitweb: http://git.kernel.org/tip/4ca4df0b7eb06df264b2919759957f6d6ea1822e Author: Bin Gao <bin.gao@xxxxxxxxxxxxxxx> AuthorDate: Tue, 15 Nov 2016 12:27:22 -0800 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitDate: Fri, 18 Nov 2016 10:58:30 +0100 x86/tsc: Mark TSC frequency determined by CPUID as known CPUs/SoCs with CPUID leaf 0x15 come with a known frequency and will report the frequency to software via CPUID instruction. This hardware provided frequency is the "real" frequency of TSC. Set the X86_FEATURE_TSC_KNOWN_FREQ flag for such systems to skip the software calibration process. A 24 hours test on one of the CPUID 0x15 capable platforms was conducted. PIT calibrated frequency resulted in more than 3 seconds drift whereas the CPUID determined frequency showed less than 0.5 second drift. Signed-off-by: Bin Gao <bin.gao@xxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/1479241644-234277-3-git-send-email-bin.gao@xxxxxxxxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> --- arch/x86/kernel/tsc.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index d2c4ee4..e58c319 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -702,6 +702,13 @@ unsigned long native_calibrate_tsc(void) } } + /* + * TSC frequency determined by CPUID is a "hardware reported" + * frequency and is the most accurate one so far we have. This + * is considered a known frequency. + */ + setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ); + return crystal_khz * ebx_numerator / eax_denominator; } -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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