[PATCH v4 01/47] x86/tsc: Never re-calibrate TSC frequency if its exact timing is known

[Sean Christopherson]

Don't re-calibrate the TSC frequency if the TSC is known to run at a fixed
frequency.  In practice, this is likely one big nop, as re-calibration is
used only for SMP=n kernels, and only for hardware that is 20+ years old,
i.e. is extremely unlikely to collide with TSC_KNOWN_FREQ.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kernel/tsc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index c5110eb554bc..08cf6625d484 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -946,7 +946,8 @@ void recalibrate_cpu_khz(void)
 		return;
 
 	cpu_khz = x86_platform.calibrate_cpu();
-	tsc_khz = x86_platform.calibrate_tsc();
+	if (!boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ))
+		tsc_khz = x86_platform.calibrate_tsc();
 	if (tsc_khz == 0)
 		tsc_khz = cpu_khz;
 	else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
-- 
2.54.0.823.g6e5bcc1fc9-goog