Merge commit '900cfa46191a7d87cf1891924cb90499287fd235'; branches 'timers/nohz',...

[cascardo/linux.git] / arch / x86 / kernel / tsc_32.c

diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
index 068759d..65b7063 100644 (file)
--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -14,7 +14,10 @@
 
 #include "mach_timer.h"
 
-static int tsc_disabled;
+/* native_sched_clock() is called before tsc_init(), so
+   we must start with the TSC soft disabled to prevent
+   erroneous rdtsc usage on !cpu_has_tsc processors */
+static int tsc_disabled = -1;
 
 /*
  * On some systems the TSC frequency does not
@@ -402,25 +405,20 @@ void __init tsc_init(void)
 {
        int cpu;
 
-       if (!cpu_has_tsc || tsc_disabled) {
-               /* Disable the TSC in case of !cpu_has_tsc */
-               tsc_disabled = 1;
+       if (!cpu_has_tsc || tsc_disabled > 0)
                return;
-       }
 
        cpu_khz = calculate_cpu_khz();
        tsc_khz = cpu_khz;
 
        if (!cpu_khz) {
                mark_tsc_unstable("could not calculate TSC khz");
-               /*
-                * We need to disable the TSC completely in this case
-                * to prevent sched_clock() from using it.
-                */
-               tsc_disabled = 1;
                return;
        }
 
+       /* now allow native_sched_clock() to use rdtsc */
+       tsc_disabled = 0;
+
        printk("Detected %lu.%03lu MHz processor.\n",
                                (unsigned long)cpu_khz / 1000,
                                (unsigned long)cpu_khz % 1000);