2 files changed, 11 insertions, 3 deletions

diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h
index bd37ed444a21..20ca9c4d4686 100644
--- a/arch/x86/include/asm/timer.h
+++ b/arch/x86/include/asm/timer.h
@@ -45,12 +45,16 @@ extern int no_timer_check;
  */
 
 DECLARE_PER_CPU(unsigned long, cyc2ns);
+DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
 
 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
 
 static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
 {
-        return cyc * per_cpu(cyc2ns, smp_processor_id()) >> CYC2NS_SCALE_FACTOR;
+        int cpu = smp_processor_id();
+        unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
+        ns += cyc * per_cpu(cyc2ns, cpu) >> CYC2NS_SCALE_FACTOR;
+        return ns;
 }
 
 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 3e1c057e98fe..ef4dac50143f 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -589,22 +589,26 @@ EXPORT_SYMBOL(recalibrate_cpu_khz);
  */
 
 DEFINE_PER_CPU(unsigned long, cyc2ns);
+DEFINE_PER_CPU(unsigned long long, cyc2ns_offset);
 
 static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
 {
-        unsigned long long tsc_now, ns_now;
+        unsigned long long tsc_now, ns_now, *offset;
         unsigned long flags, *scale;
 
         local_irq_save(flags);
         sched_clock_idle_sleep_event();
 
         scale = &per_cpu(cyc2ns, cpu);
+        offset = &per_cpu(cyc2ns_offset, cpu);
 
         rdtscll(tsc_now);
         ns_now = __cycles_2_ns(tsc_now);
 
-        if (cpu_khz)
+        if (cpu_khz) {
                 *scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
+                *offset = ns_now - (tsc_now * *scale >> CYC2NS_SCALE_FACTOR);
+        }
 
         sched_clock_idle_wakeup_event(0);
         local_irq_restore(flags);