1 files changed, 58 insertions, 37 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 52284d31fc9c..da033b5b3e19 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -159,9 +159,14 @@ static unsigned long calc_pmtimer_ref(u64 deltatsc, u64 pm1, u64 pm2)
         return (unsigned long) deltatsc;
 }
 
-#define CAL_MS          50
+#define CAL_MS          10
 #define CAL_LATCH       (CLOCK_TICK_RATE / (1000 / CAL_MS))
-#define CAL_PIT_LOOPS   5000
+#define CAL_PIT_LOOPS   1000
+
+#define CAL2_MS         50
+#define CAL2_LATCH      (CLOCK_TICK_RATE / (1000 / CAL2_MS))
+#define CAL2_PIT_LOOPS  5000
+
 
 /*
  * Try to calibrate the TSC against the Programmable
@@ -170,7 +175,7 @@ static unsigned long calc_pmtimer_ref(u64 deltatsc, u64 pm1, u64 pm2)
  *
  * Return ULONG_MAX on failure to calibrate.
  */
-static unsigned long pit_calibrate_tsc(void)
+static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin)
 {
         u64 tsc, t1, t2, delta;
         unsigned long tscmin, tscmax;
@@ -185,8 +190,8 @@ static unsigned long pit_calibrate_tsc(void)
          * (LSB then MSB) to begin countdown.
          */
         outb(0xb0, 0x43);
-        outb(CAL_LATCH & 0xff, 0x42);
-        outb(CAL_LATCH >> 8, 0x42);
+        outb(latch & 0xff, 0x42);
+        outb(latch >> 8, 0x42);
 
         tsc = t1 = t2 = get_cycles();
 
@@ -207,18 +212,18 @@ static unsigned long pit_calibrate_tsc(void)
         /*
          * Sanity checks:
          *
-         * If we were not able to read the PIT more than PIT_MIN_LOOPS
+         * If we were not able to read the PIT more than loopmin
          * times, then we have been hit by a massive SMI
          *
          * If the maximum is 10 times larger than the minimum,
          * then we got hit by an SMI as well.
          */
-        if (pitcnt < CAL_PIT_LOOPS || tscmax > 10 * tscmin)
+        if (pitcnt < loopmin || tscmax > 10 * tscmin)
                 return ULONG_MAX;
 
         /* Calculate the PIT value */
         delta = t2 - t1;
-        do_div(delta, CAL_MS);
+        do_div(delta, ms);
         return delta;
 }
 
@@ -230,8 +235,8 @@ unsigned long native_calibrate_tsc(void)
 {
         u64 tsc1, tsc2, delta, ref1, ref2;
         unsigned long tsc_pit_min = ULONG_MAX, tsc_ref_min = ULONG_MAX;
-        unsigned long flags;
-        int hpet = is_hpet_enabled(), i;
+        unsigned long flags, latch, ms;
+        int hpet = is_hpet_enabled(), i, loopmin;
 
         /*
          * Run 5 calibration loops to get the lowest frequency value
@@ -257,7 +262,13 @@ unsigned long native_calibrate_tsc(void)
          * calibration delay loop as we have to wait for a certain
          * amount of time anyway.
          */
-        for (i = 0; i < 5; i++) {
+
+        /* Preset PIT loop values */
+        latch = CAL_LATCH;
+        ms = CAL_MS;
+        loopmin = CAL_PIT_LOOPS;
+
+        for (i = 0; i < 3; i++) {
                 unsigned long tsc_pit_khz;
 
                 /*
@@ -268,7 +279,7 @@ unsigned long native_calibrate_tsc(void)
                  */
                 local_irq_save(flags);
                 tsc1 = tsc_read_refs(&ref1, hpet);
-                tsc_pit_khz = pit_calibrate_tsc();
+                tsc_pit_khz = pit_calibrate_tsc(latch, ms, loopmin);
                 tsc2 = tsc_read_refs(&ref2, hpet);
                 local_irq_restore(flags);
 
@@ -290,6 +301,35 @@ unsigned long native_calibrate_tsc(void)
                         tsc2 = calc_pmtimer_ref(tsc2, ref1, ref2);
 
                 tsc_ref_min = min(tsc_ref_min, (unsigned long) tsc2);
+
+                /* Check the reference deviation */
+                delta = ((u64) tsc_pit_min) * 100;
+                do_div(delta, tsc_ref_min);
+
+                /*
+                 * If both calibration results are inside a 10% window
+                 * then we can be sure, that the calibration
+                 * succeeded. We break out of the loop right away. We
+                 * use the reference value, as it is more precise.
+                 */
+                if (delta >= 90 && delta <= 110) {
+                        printk(KERN_INFO
+                               "TSC: PIT calibration matches %s. %d loops\n",
+                               hpet ? "HPET" : "PMTIMER", i + 1);
+                        return tsc_ref_min;
+                }
+
+                /*
+                 * Check whether PIT failed more than once. This
+                 * happens in virtualized environments. We need to
+                 * give the virtual PC a slightly longer timeframe for
+                 * the HPET/PMTIMER to make the result precise.
+                 */
+                if (i == 1 && tsc_pit_min == ULONG_MAX) {
+                        latch = CAL2_LATCH;
+                        ms = CAL2_MS;
+                        loopmin = CAL2_PIT_LOOPS;
+                }
         }
 
         /*
@@ -309,7 +349,7 @@ unsigned long native_calibrate_tsc(void)
                 /* The alternative source failed as well, disable TSC */
                 if (tsc_ref_min == ULONG_MAX) {
                         printk(KERN_WARNING "TSC: HPET/PMTIMER calibration "
-                               "failed due to SMI disturbance.\n");
+                               "failed.\n");
                         return 0;
                 }
 
@@ -328,37 +368,18 @@ unsigned long native_calibrate_tsc(void)
 
         /* The alternative source failed, use the PIT calibration value */
         if (tsc_ref_min == ULONG_MAX) {
-                printk(KERN_WARNING "TSC: HPET/PMTIMER calibration failed due "
-                       "to SMI disturbance. Using PIT calibration\n");
+                printk(KERN_WARNING "TSC: HPET/PMTIMER calibration failed. "
+                       "Using PIT calibration\n");
                 return tsc_pit_min;
         }
 
-        /* Check the reference deviation */
-        delta = ((u64) tsc_pit_min) * 100;
-        do_div(delta, tsc_ref_min);
-
-        /*
-         * If both calibration results are inside a 5% window, the we
-         * use the lower frequency of those as it is probably the
-         * closest estimate.
-         */
-        if (delta >= 95 && delta <= 105) {
-                printk(KERN_INFO "TSC: PIT calibration confirmed by %s.\n",
-                       hpet ? "HPET" : "PMTIMER");
-                printk(KERN_INFO "TSC: using %s calibration value\n",
-                       tsc_pit_min <= tsc_ref_min ? "PIT" :
-                       hpet ? "HPET" : "PMTIMER");
-                return tsc_pit_min <= tsc_ref_min ? tsc_pit_min : tsc_ref_min;
-        }
-
-        printk(KERN_WARNING "TSC: PIT calibration deviates from %s: %lu %lu.\n",
-               hpet ? "HPET" : "PMTIMER", tsc_pit_min, tsc_ref_min);
-
         /*
          * The calibration values differ too much. In doubt, we use
          * the PIT value as we know that there are PMTIMERs around
-         * running at double speed.
+         * running at double speed. At least we let the user know:
          */
+        printk(KERN_WARNING "TSC: PIT calibration deviates from %s: %lu %lu.\n",
+               hpet ? "HPET" : "PMTIMER", tsc_pit_min, tsc_ref_min);
         printk(KERN_INFO "TSC: Using PIT calibration value\n");
         return tsc_pit_min;
 }