1 files changed, 6 insertions, 8 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 2c9cf0fd78f5..f54694611172 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -290,14 +290,15 @@ static inline int pit_verify_msb(unsigned char val)
 static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap)
 {
         int count;
-        u64 tsc = 0;
+        u64 tsc = 0, prev_tsc = 0;
 
         for (count = 0; count < 50000; count++) {
                 if (!pit_verify_msb(val))
                         break;
+                prev_tsc = tsc;
                 tsc = get_cycles();
         }
-        *deltap = get_cycles() - tsc;
+        *deltap = get_cycles() - prev_tsc;
         *tscp = tsc;
 
         /*
@@ -311,9 +312,9 @@ static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *de
  * How many MSB values do we want to see? We aim for
  * a maximum error rate of 500ppm (in practice the
  * real error is much smaller), but refuse to spend
- * more than 25ms on it.
+ * more than 50ms on it.
  */
-#define MAX_QUICK_PIT_MS 25
+#define MAX_QUICK_PIT_MS 50
 #define MAX_QUICK_PIT_ITERATIONS (MAX_QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256)
 
 static unsigned long quick_pit_calibrate(void)
@@ -383,15 +384,12 @@ success:
          *
          * As a result, we can depend on there not being
          * any odd delays anywhere, and the TSC reads are
-         * reliable (within the error). We also adjust the
-         * delta to the middle of the error bars, just
-         * because it looks nicer.
+         * reliable (within the error).
          *
          * kHz = ticks / time-in-seconds / 1000;
          * kHz = (t2 - t1) / (I * 256 / PIT_TICK_RATE) / 1000
          * kHz = ((t2 - t1) * PIT_TICK_RATE) / (I * 256 * 1000)
          */
-        delta += (long)(d2 - d1)/2;
         delta *= PIT_TICK_RATE;
         do_div(delta, i*256*1000);
         printk("Fast TSC calibration using PIT\n");