1 files changed, 18 insertions, 8 deletions

diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index 2cfc7b09b925..46f752a8bbf3 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -23,6 +23,7 @@
  * an extra value to store the TSC freq
  */
 unsigned int tsc_khz;
+unsigned long long (*custom_sched_clock)(void);
 
 int tsc_disable;
 
@@ -107,14 +108,14 @@ unsigned long long sched_clock(void)
 {
         unsigned long long this_offset;
 
+        if (unlikely(custom_sched_clock))
+                return (*custom_sched_clock)();
+
         /*
-         * in the NUMA case we dont use the TSC as they are not
-         * synchronized across all CPUs.
+         * Fall back to jiffies if there's no TSC available:
          */
-#ifndef CONFIG_NUMA
-        if (!cpu_khz || check_tsc_unstable())
-#endif
-                /* no locking but a rare wrong value is not a big deal */
+        if (unlikely(tsc_disable))
+                /* No locking but a rare wrong value is not a big deal: */
                 return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 
         /* read the Time Stamp Counter: */
@@ -194,13 +195,13 @@ EXPORT_SYMBOL(recalibrate_cpu_khz);
 void __init tsc_init(void)
 {
         if (!cpu_has_tsc || tsc_disable)
-                return;
+                goto out_no_tsc;
 
         cpu_khz = calculate_cpu_khz();
         tsc_khz = cpu_khz;
 
         if (!cpu_khz)
-                return;
+                goto out_no_tsc;
 
         printk("Detected %lu.%03lu MHz processor.\n",
                                 (unsigned long)cpu_khz / 1000,
@@ -208,6 +209,15 @@ void __init tsc_init(void)
 
         set_cyc2ns_scale(cpu_khz);
         use_tsc_delay();
+        return;
+
+out_no_tsc:
+        /*
+         * Set the tsc_disable flag if there's no TSC support, this
+         * makes it a fast flag for the kernel to see whether it
+         * should be using the TSC.
+         */
+        tsc_disable = 1;
 }
 
 #ifdef CONFIG_CPU_FREQ