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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2008-08-25 17:15:34 +0200
committerIngo Molnar <mingo@elte.hu>2008-08-25 17:39:57 +0200
commit354879bb977e06695993435745f06a0f6d39ce2b (patch)
treeb811b4ec423fac8bdb671dafbf422aa4245bdcb3 /kernel/sched_clock.c
parentefc2dead2c82cae31943828f6d977c483942b0eb (diff)
downloadlinux-stericsson-354879bb977e06695993435745f06a0f6d39ce2b.tar.gz
sched_clock: fix cpu_clock()
This patch fixes 3 issues: a) it removes the dependency on jiffies, because jiffies are incremented by a single CPU, and the tick is not synchronized between CPUs. Therefore relying on it to calculate a window to clip whacky TSC values doesn't work as it can drift around. So instead use [GTOD, GTOD+TICK_NSEC) as the window. b) __update_sched_clock() did (roughly speaking): delta = sched_clock() - scd->tick_raw; clock += delta; Which gives exponential growth, instead of linear. c) allows the sched_clock_cpu() value to warp the u64 without breaking. the results are more reliable sched_clock() deltas: before after sched_clock cpu_clock: 15750 51312 51488 cpu_clock: 59719 51052 50947 cpu_clock: 15879 51249 51061 cpu_clock: 1 50933 51198 cpu_clock: 1 50931 51039 cpu_clock: 1 51093 50981 cpu_clock: 1 51043 51040 cpu_clock: 1 50959 50938 cpu_clock: 1 50981 51011 cpu_clock: 1 51364 51212 cpu_clock: 1 51219 51273 cpu_clock: 1 51389 51048 cpu_clock: 1 51285 51611 cpu_clock: 1 50964 51137 cpu_clock: 1 50973 50968 cpu_clock: 1 50967 50972 cpu_clock: 1 58910 58485 cpu_clock: 1 51082 51025 cpu_clock: 1 50957 50958 cpu_clock: 1 50958 50957 cpu_clock: 1006128 51128 50971 cpu_clock: 1 51107 51155 cpu_clock: 1 51371 51081 cpu_clock: 1 51104 51365 cpu_clock: 1 51363 51309 cpu_clock: 1 51107 51160 cpu_clock: 1 51139 51100 cpu_clock: 1 51216 51136 cpu_clock: 1 51207 51215 cpu_clock: 1 51087 51263 cpu_clock: 1 51249 51177 cpu_clock: 1 51519 51412 cpu_clock: 1 51416 51255 cpu_clock: 1 51591 51594 cpu_clock: 1 50966 51374 cpu_clock: 1 50966 50966 cpu_clock: 1 51291 50948 cpu_clock: 1 50973 50867 cpu_clock: 1 50970 50970 cpu_clock: 998306 50970 50971 cpu_clock: 1 50971 50970 cpu_clock: 1 50970 50970 cpu_clock: 1 50971 50971 cpu_clock: 1 50970 50970 cpu_clock: 1 51351 50970 cpu_clock: 1 50970 51352 cpu_clock: 1 50971 50970 cpu_clock: 1 50970 50970 cpu_clock: 1 51321 50971 cpu_clock: 1 50974 51324 Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched_clock.c')
-rw-r--r--kernel/sched_clock.c84
1 files changed, 34 insertions, 50 deletions
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 204991a0bfa7..e8ab096ddfe3 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);