[git pull] scheduler fixes

Ingo Molnar
2008-08-25T17:37:39Z

Linus,

Please pull the latest sched-fixes-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git sched-fixes-for-linus

This has a fix from Peter that is fresh (from earlier today) but i'm
pushing it because it would be nice to have it in -rc5 and it looks
fairly safe as well.

Thanks,

Ingo

------------------>
Peter Zijlstra (1):
sched_clock: fix cpu_clock()

kernel/sched_clock.c | 84 ++++++++++++++++++++-----------------------------
1 files changed, 34 insertions(+), 50 deletions(-)

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 204991a..e8ab096 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -12,19 +12,17 @@
*
* Create a semi stable clock from a mixture of other events, including:
* - gtod
- * - jiffies
* - sched_clock()
* - explicit idle events
*
* We use gtod as base and the unstable clock deltas. The deltas are filtered,
- * making it monotonic and keeping it within an expected window. This window
- * is set up using jiffies.
+ * making it monotonic and keeping it within an expected window.
*
* Furthermore, explicit sleep and wakeup hooks allow us to account for time
* that is otherwise invisible (TSC gets stopped).
*
* The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
- * consistent between cpus (never more than 1 jiffies difference).
+ * consistent between cpus (never more than 2 jiffies difference).
*/
#include <linux/sched.h>
#include <linux/percpu.h>
@@ -54,7 +52,6 @@ struct sched_clock_data {
*/
raw_spinlock_t lock;

- unsigned long tick_jiffies;
u64 tick_raw;
u64 tick_gtod;
u64 clock;
@@ -75,14 +72,12 @@ static inline struct sched_clock_data *cpu_sdc(int cpu)
void sched_clock_init(void)
{
u64 ktime_now = ktime_to_ns(ktime_get());
- unsigned long now_jiffies = jiffies;
int cpu;

for_each_possible_cpu(cpu) {
struct sched_clock_data *scd = cpu_sdc(cpu);

scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
- scd->tick_jiffies = now_jiffies;
scd->tick_raw = 0;
scd->tick_gtod = ktime_now;
scd->clock = ktime_now;
@@ -92,46 +87,51 @@ void sched_clock_init(void)
}

/*
+ * min,max except they take wrapping into account
+ */
+
+static inline u64 wrap_min(u64 x, u64 y)
+{
+ return (s64)(x - y) < 0 ? x : y;
+}
+
+static inline u64 wrap_max(u64 x, u64 y)
+{
+ return (s64)(x - y) > 0 ? x : y;
+}
+
+/*
* update the percpu scd from the raw @now value
*
* - filter out backward motion
- * - use jiffies to generate a min,max window to clip the raw values
+ * - use the GTOD tick value to create a window to filter crazy TSC values
*/
static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
{
- unsigned long now_jiffies = jiffies;
- long delta_jiffies = now_jiffies - scd->tick_jiffies;
- u64 clock = scd->clock;
- u64 min_clock, max_clock;
s64 delta = now - scd->tick_raw;
+ u64 clock, min_clock, max_clock;

WARN_ON_ONCE(!irqs_disabled());
- min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;

- if (unlikely(delta < 0)) {
- clock++;
- goto out;
- }
+ if (unlikely(delta < 0))
+ delta = 0;

- max_clock = min_clock + TICK_NSEC;
+ /*
+ * scd->clock = clamp(scd->tick_gtod + delta,
+ * max(scd->tick_gtod, scd->clock),
+ * scd->tick_gtod + TICK_NSEC);
+ */

- if (unlikely(clock + delta > max_clock)) {
- if (clock < max_clock)
- clock = max_clock;
- else
- clock++;
- } else {
- clock += delta;
- }
+ clock = scd->tick_gtod + delta;
+ min_clock = wrap_max(scd->tick_gtod, scd->clock);
+ max_clock = scd->tick_gtod + TICK_NSEC;

- out:
- if (unlikely(clock < min_clock))
- clock = min_clock;
+ clock = wrap_max(clock, min_clock);
+ clock = wrap_min(clock, max_clock);

- scd->tick_jiffies = now_jiffies;
scd->clock = clock;

- return clock;
+ return scd->clock;
}

static void lock_double_clock(struct sched_clock_data *data1,
@@ -171,7 +171,7 @@ u64 sched_clock_cpu(int cpu)
* larger time as the latest time for both
* runqueues. (this creates monotonic movement)
*/
- if (likely(remote_clock < this_clock)) {
+ if (likely((s64)(remote_clock - this_clock) < 0)) {
clock = this_clock;
scd->clock = clock;
} else {
@@ -207,14 +207,9 @@ void sched_clock_tick(void)
now = sched_clock();

__raw_spin_lock(&scd->lock);
- __update_sched_clock(scd, now);
- /*
- * update tick_gtod after __update_sched_clock() because that will
- * already observe 1 new jiffy; adding a new tick_gtod to that would
- * increase the clock 2 jiffies.
- */
scd->tick_raw = now;
scd->tick_gtod = now_gtod;
+ __update_sched_clock(scd, now);
__raw_spin_unlock(&scd->lock);
}

@@ -232,18 +227,7 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
*/
void sched_clock_idle_wakeup_event(u64 delta_ns)
{
- struct sched_clock_data *scd = this_scd();
-
- /*
- * Override the previous timestamp and ignore all
- * sched_clock() deltas that occured while we idled,
- * and use the PM-provided delta_ns to advance the
- * rq clock:
- */
- __raw_spin_lock(&scd->lock);
- scd->clock += delta_ns;
- __raw_spin_unlock(&scd->lock);
-
+ sched_clock_tick();
touch_softlockup_watchdog();
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);