1 files changed, 12 insertions, 4 deletions

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index e0341c6808e5..7a9b18224182 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -28,6 +28,7 @@
 #include <linux/acpi.h>
 #ifdef CONFIG_ACPI
 #include <acpi/achware.h>       /* for PM timer frequency */
+#include <acpi/acpi_bus.h>
 #endif
 #include <asm/8253pit.h>
 #include <asm/pgtable.h>
@@ -953,11 +954,18 @@ __cpuinit int unsynchronized_tsc(void)
 #ifdef CONFIG_SMP
         if (apic_is_clustered_box())
                 return 1;
-        /* Intel systems are normally all synchronized. Exceptions
-           are handled in the check above. */
-        if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
-                return 0;
 #endif
+        /* Most intel systems have synchronized TSCs except for
+           multi node systems */
+        if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
+#ifdef CONFIG_ACPI
+                /* But TSC doesn't tick in C3 so don't use it there */
+                if (acpi_fadt.length > 0 && acpi_fadt.plvl3_lat < 100)
+                        return 1;
+#endif
+                return 0;
+        }
+
         /* Assume multi socket systems are not synchronized */
         return num_present_cpus() > 1;
 }