sched_clock: and multiplier for TSC to gtod drift

[linux-2.6-omap-h63xx.git] / kernel / sched_clock.c

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 28ff6bf5e02b9697657bed07941a98ddae88fa0e..8affbfd0cdb0fda3aa3679c8a0a7960671dbf13b 100644 (file)
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -3,6 +3,9 @@
  *
  *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
  *
+ *  Updates and enhancements:
+ *    Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
+ *
  * Based on code by:
  *   Ingo Molnar <mingo@redhat.com>
  *   Guillaume Chazarain <guichaz@gmail.com>
@@ -32,6 +35,11 @@
 
 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
 
+#define MULTI_SHIFT 15
+/* Max is double, Min is 1/2 */
+#define MAX_MULTI (2LL << MULTI_SHIFT)
+#define MIN_MULTI (1LL << (MULTI_SHIFT-1))
+
 struct sched_clock_data {
        /*
         * Raw spinlock - this is a special case: this might be called
@@ -45,6 +53,7 @@ struct sched_clock_data {
        u64                     tick_raw;
        u64                     tick_gtod;
        u64                     clock;
+       s64                     multi;
 #ifdef CONFIG_NO_HZ
        int                     check_max;
 #endif
@@ -79,6 +88,7 @@ void sched_clock_init(void)
                scd->tick_raw = 0;
                scd->tick_gtod = ktime_now;
                scd->clock = ktime_now;
+               scd->multi = 1 << MULTI_SHIFT;
 #ifdef CONFIG_NO_HZ
                scd->check_max = 1;
 #endif
@@ -134,8 +144,13 @@ static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *tim
 
        WARN_ON_ONCE(!irqs_disabled());
 
-       min_clock = scd->tick_gtod +
-               (delta_jiffies ? delta_jiffies - 1 : 0) * TICK_NSEC;
+       /*
+        * At schedule tick the clock can be just under the gtod. We don't
+        * want to push it too prematurely.
+        */
+       min_clock = scd->tick_gtod + (delta_jiffies * TICK_NSEC);
+       if (min_clock > TICK_NSEC)
+               min_clock -= TICK_NSEC / 2;
 
        if (unlikely(delta < 0)) {
                clock++;
@@ -149,6 +164,9 @@ static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *tim
         */
        max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
 
+       delta *= scd->multi;
+       delta >>= MULTI_SHIFT;
+
        if (unlikely(clock + delta > max_clock) && check_max(scd)) {
                if (clock < max_clock)
                        clock = max_clock;
@@ -230,6 +248,7 @@ void sched_clock_tick(void)
 {
        struct sched_clock_data *scd = this_scd();
        unsigned long now_jiffies = jiffies;
+       s64 mult, delta_gtod, delta_raw;
        u64 now, now_gtod;
 
        if (unlikely(!sched_clock_running))
@@ -247,9 +266,23 @@ void sched_clock_tick(void)
         * already observe 1 new jiffy; adding a new tick_gtod to that would
         * increase the clock 2 jiffies.
         */
-       scd->tick_jiffies = now_jiffies;
+       delta_gtod = now_gtod - scd->tick_gtod;
+       delta_raw = now - scd->tick_raw;
+
+       if ((long)delta_raw > 0) {
+               mult = delta_gtod << MULTI_SHIFT;
+               do_div(mult, delta_raw);
+               scd->multi = mult;
+               if (scd->multi > MAX_MULTI)
+                       scd->multi = MAX_MULTI;
+               else if (scd->multi < MIN_MULTI)
+                       scd->multi = MIN_MULTI;
+       } else
+               scd->multi = 1 << MULTI_SHIFT;
+
        scd->tick_raw = now;
        scd->tick_gtod = now_gtod;
+       scd->tick_jiffies = now_jiffies;
        __raw_spin_unlock(&scd->lock);
 }
 
@@ -279,6 +312,7 @@ void sched_clock_idle_wakeup_event(u64 delta_ns)
        __raw_spin_lock(&scd->lock);
        scd->prev_raw = now;
        scd->clock += delta_ns;
+       scd->multi = 1 << MULTI_SHIFT;
        __raw_spin_unlock(&scd->lock);
 
        touch_softlockup_watchdog();