[05/17] Keep SMP VMs more in sync on unstable TSC

Commit Message

Zachary Amsden June 15, 2010, 7:34 a.m. UTC

None

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 94f6ce8..1afecd7 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -337,6 +337,7 @@  struct kvm_vcpu_arch {
 	unsigned int time_offset;
 	struct page *time_page;
 	u64 last_host_tsc;
+	u64 last_host_ns;
 
 	bool nmi_pending;
 	bool nmi_injected;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 618c435..b1bdf05 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1810,6 +1810,19 @@  void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 		/* Make sure TSC doesn't go backwards */
 		s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 : 
 				native_read_tsc() - vcpu->arch.last_host_tsc;
+
+		/* Subtract elapsed cycle time from the delta computation */
+		if (check_tsc_unstable() && vcpu->arch.last_host_ns) {
+			s64 delta;
+			struct timespec ts;
+			ktime_get_ts(&ts);
+			monotonic_to_bootbased(&ts);
+			delta = timespec_to_ns(&ts) - vcpu->arch.last_host_ns;
+			delta = delta * per_cpu(cpu_tsc_khz, cpu);
+			delta = delta / USEC_PER_SEC;
+			tsc_delta -= delta;
+		}
+
 		if (tsc_delta < 0 || check_tsc_unstable())
 			kvm_x86_ops->adjust_tsc_offset(vcpu, -tsc_delta);
 		kvm_migrate_timers(vcpu);
@@ -1832,8 +1845,13 @@  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	 * vcpu->cpu != cpu can not detect this condition.  So set
 	 * vcpu->cpu = -1 to force the recalibration above.
 	 */
-	if (check_tsc_unstable())
+	if (check_tsc_unstable()) {
+		struct timespec ts;
+		ktime_get_ts(&ts);
+		monotonic_to_bootbased(&ts);
+		vcpu->arch.last_host_ns = timespec_to_ns(&ts);
 		vcpu->cpu = -1;
+	}
 }
 
 static int is_efer_nx(void)