提交 47c95a46 编写于 作者: B Bin Gao 提交者: Thomas Gleixner

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: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NBin 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.comSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
上级 a25f0944
......@@ -106,6 +106,7 @@
#define X86_FEATURE_APERFMPERF ( 3*32+28) /* APERFMPERF */
#define X86_FEATURE_EAGER_FPU ( 3*32+29) /* "eagerfpu" Non lazy FPU restore */
#define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */
#define X86_FEATURE_TSC_KNOWN_FREQ ( 3*32+31) /* TSC has known frequency */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 ( 4*32+ 0) /* "pni" SSE-3 */
......
......@@ -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;
}
......
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