Merge branches 'sched/cleanups' and 'linus' into sched/core

diff --combined arch/x86/kernel/tsc.c
index 9c8b715,d5cebb5..dfa6f7b
--- 1/arch/x86/kernel/tsc.c
--- 2/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@@ -17,21 -17,20 +17,21 @@@
  #include <asm/delay.h>
  #include <asm/hypervisor.h>
  
 -unsigned int cpu_khz;           /* TSC clocks / usec, not used here */
 +unsigned int __read_mostly cpu_khz;   /* TSC clocks / usec, not used here */
  EXPORT_SYMBOL(cpu_khz);
 -unsigned int tsc_khz;
 +
 +unsigned int __read_mostly tsc_khz;
  EXPORT_SYMBOL(tsc_khz);
  
  /*
   * TSC can be unstable due to cpufreq or due to unsynced TSCs
   */
 -static int tsc_unstable;
 +static int __read_mostly tsc_unstable;
  
  /* 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;
 +static int __read_mostly tsc_disabled = -1;
  
  static int tsc_clocksource_reliable;
  /*
@@@ -274,30 -273,43 +274,43 @@@ static unsigned long pit_calibrate_tsc(
   * use the TSC value at the transitions to calculate a pretty
   * good value for the TSC frequencty.
   */
- static inline int pit_expect_msb(unsigned char val)
+ static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap)
  {
-       int count = 0;
+       int count;
+       u64 tsc = 0;
  
        for (count = 0; count < 50000; count++) {
                /* Ignore LSB */
                inb(0x42);
                if (inb(0x42) != val)
                        break;
+               tsc = get_cycles();
        }
-       return count > 50;
+       *deltap = get_cycles() - tsc;
+       *tscp = tsc;
+ 
+       /*
+        * We require _some_ success, but the quality control
+        * will be based on the error terms on the TSC values.
+        */
+       return count > 5;
  }
  
  /*
-  * How many MSB values do we want to see? We aim for a
-  * 15ms calibration, which assuming a 2us counter read
-  * error should give us roughly 150 ppm precision for
-  * the calibration.
+  * 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.
   */
- #define QUICK_PIT_MS 15
- #define QUICK_PIT_ITERATIONS (QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256)
+ #define MAX_QUICK_PIT_MS 25
+ #define MAX_QUICK_PIT_ITERATIONS (MAX_QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256)
  
  static unsigned long quick_pit_calibrate(void)
  {
+       int i;
+       u64 tsc, delta;
+       unsigned long d1, d2;
+ 
        /* Set the Gate high, disable speaker */
        outb((inb(0x61) & ~0x02) | 0x01, 0x61);
  
@@@ -316,45 -328,52 +329,52 @@@
        outb(0xff, 0x42);
        outb(0xff, 0x42);
  
-       if (pit_expect_msb(0xff)) {
-               int i;
-               u64 t1, t2, delta;
-               unsigned char expect = 0xfe;
- 
-               t1 = get_cycles();
-               for (i = 0; i < QUICK_PIT_ITERATIONS; i++, expect--) {
-                       if (!pit_expect_msb(expect))
-                               goto failed;
+       /*
+        * The PIT starts counting at the next edge, so we
+        * need to delay for a microsecond. The easiest way
+        * to do that is to just read back the 16-bit counter
+        * once from the PIT.
+        */
+       inb(0x42);
+       inb(0x42);
+ 
+       if (pit_expect_msb(0xff, &tsc, &d1)) {
+               for (i = 1; i <= MAX_QUICK_PIT_ITERATIONS; i++) {
+                       if (!pit_expect_msb(0xff-i, &delta, &d2))
+                               break;
+ 
+                       /*
+                        * Iterate until the error is less than 500 ppm
+                        */
+                       delta -= tsc;
+                       if (d1+d2 < delta >> 11)
+                               goto success;
                }
-               t2 = get_cycles();
- 
-               /*
-                * Make sure we can rely on the second TSC timestamp:
-                */
-               if (!pit_expect_msb(expect))
-                       goto failed;
- 
-               /*
-                * Ok, if we get here, then we've seen the
-                * MSB of the PIT decrement QUICK_PIT_ITERATIONS
-                * times, and each MSB had many hits, so we never
-                * had any sudden jumps.
-                *
-                * As a result, we can depend on there not being
-                * any odd delays anywhere, and the TSC reads are
-                * reliable.
-                *
-                * kHz = ticks / time-in-seconds / 1000;
-                * kHz = (t2 - t1) / (QPI * 256 / PIT_TICK_RATE) / 1000
-                * kHz = ((t2 - t1) * PIT_TICK_RATE) / (QPI * 256 * 1000)
-                */
-               delta = (t2 - t1)*PIT_TICK_RATE;
-               do_div(delta, QUICK_PIT_ITERATIONS*256*1000);
-               printk("Fast TSC calibration using PIT\n");
-               return delta;
        }
- failed:
+       printk("Fast TSC calibration failed\n");
        return 0;
+ 
+ success:
+       /*
+        * Ok, if we get here, then we've seen the
+        * MSB of the PIT decrement 'i' times, and the
+        * error has shrunk to less than 500 ppm.
+        *
+        * 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.
+        *
+        * 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");
+       return delta;
  }
  
  /**