summaryrefslogtreecommitdiffstats
path: root/arch/x86_64/kernel/time.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86_64/kernel/time.c')
-rw-r--r--arch/x86_64/kernel/time.c16
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;
}