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Diffstat (limited to 'arch/x86/kernel/kvmclock.c')
-rw-r--r--arch/x86/kernel/kvmclock.c20
1 files changed, 15 insertions, 5 deletions
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index e811d4d1c824..904494b924c1 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -104,12 +104,8 @@ static u64 kvm_sched_clock_read(void)
static inline void kvm_sched_clock_init(bool stable)
{
- if (!stable) {
- pv_ops.time.sched_clock = kvm_clock_read;
+ if (!stable)
clear_sched_clock_stable();
- return;
- }
-
kvm_sched_clock_offset = kvm_clock_read();
pv_ops.time.sched_clock = kvm_sched_clock_read;
@@ -355,6 +351,20 @@ void __init kvmclock_init(void)
machine_ops.crash_shutdown = kvm_crash_shutdown;
#endif
kvm_get_preset_lpj();
+
+ /*
+ * X86_FEATURE_NONSTOP_TSC is TSC runs at constant rate
+ * with P/T states and does not stop in deep C-states.
+ *
+ * Invariant TSC exposed by host means kvmclock is not necessary:
+ * can use TSC as clocksource.
+ *
+ */
+ if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+ boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
+ !check_tsc_unstable())
+ kvm_clock.rating = 299;
+
clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
pv_info.name = "KVM";
}