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>
This commit is contained in:
parent
efc2dead2c
commit
354879bb97
|
@ -12,19 +12,17 @@
|
||||||
*
|
*
|
||||||
* Create a semi stable clock from a mixture of other events, including:
|
* Create a semi stable clock from a mixture of other events, including:
|
||||||
* - gtod
|
* - gtod
|
||||||
* - jiffies
|
|
||||||
* - sched_clock()
|
* - sched_clock()
|
||||||
* - explicit idle events
|
* - explicit idle events
|
||||||
*
|
*
|
||||||
* We use gtod as base and the unstable clock deltas. The deltas are filtered,
|
* 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
|
* making it monotonic and keeping it within an expected window.
|
||||||
* is set up using jiffies.
|
|
||||||
*
|
*
|
||||||
* Furthermore, explicit sleep and wakeup hooks allow us to account for time
|
* Furthermore, explicit sleep and wakeup hooks allow us to account for time
|
||||||
* that is otherwise invisible (TSC gets stopped).
|
* that is otherwise invisible (TSC gets stopped).
|
||||||
*
|
*
|
||||||
* The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
|
* 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/sched.h>
|
||||||
#include <linux/percpu.h>
|
#include <linux/percpu.h>
|
||||||
|
@ -54,7 +52,6 @@ struct sched_clock_data {
|
||||||
*/
|
*/
|
||||||
raw_spinlock_t lock;
|
raw_spinlock_t lock;
|
||||||
|
|
||||||
unsigned long tick_jiffies;
|
|
||||||
u64 tick_raw;
|
u64 tick_raw;
|
||||||
u64 tick_gtod;
|
u64 tick_gtod;
|
||||||
u64 clock;
|
u64 clock;
|
||||||
|
@ -75,14 +72,12 @@ static inline struct sched_clock_data *cpu_sdc(int cpu)
|
||||||
void sched_clock_init(void)
|
void sched_clock_init(void)
|
||||||
{
|
{
|
||||||
u64 ktime_now = ktime_to_ns(ktime_get());
|
u64 ktime_now = ktime_to_ns(ktime_get());
|
||||||
unsigned long now_jiffies = jiffies;
|
|
||||||
int cpu;
|
int cpu;
|
||||||
|
|
||||||
for_each_possible_cpu(cpu) {
|
for_each_possible_cpu(cpu) {
|
||||||
struct sched_clock_data *scd = cpu_sdc(cpu);
|
struct sched_clock_data *scd = cpu_sdc(cpu);
|
||||||
|
|
||||||
scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
|
scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
|
||||||
scd->tick_jiffies = now_jiffies;
|
|
||||||
scd->tick_raw = 0;
|
scd->tick_raw = 0;
|
||||||
scd->tick_gtod = ktime_now;
|
scd->tick_gtod = ktime_now;
|
||||||
scd->clock = ktime_now;
|
scd->clock = ktime_now;
|
||||||
|
@ -91,47 +86,52 @@ void sched_clock_init(void)
|
||||||
sched_clock_running = 1;
|
sched_clock_running = 1;
|
||||||
}
|
}
|
||||||
|
|
||||||
|
/*
|
||||||
|
* 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
|
* update the percpu scd from the raw @now value
|
||||||
*
|
*
|
||||||
* - filter out backward motion
|
* - 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)
|
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;
|
s64 delta = now - scd->tick_raw;
|
||||||
|
u64 clock, min_clock, max_clock;
|
||||||
|
|
||||||
WARN_ON_ONCE(!irqs_disabled());
|
WARN_ON_ONCE(!irqs_disabled());
|
||||||
min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
|
|
||||||
|
|
||||||
if (unlikely(delta < 0)) {
|
if (unlikely(delta < 0))
|
||||||
clock++;
|
delta = 0;
|
||||||
goto out;
|
|
||||||
}
|
|
||||||
|
|
||||||
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)) {
|
clock = scd->tick_gtod + delta;
|
||||||
if (clock < max_clock)
|
min_clock = wrap_max(scd->tick_gtod, scd->clock);
|
||||||
clock = max_clock;
|
max_clock = scd->tick_gtod + TICK_NSEC;
|
||||||
else
|
|
||||||
clock++;
|
|
||||||
} else {
|
|
||||||
clock += delta;
|
|
||||||
}
|
|
||||||
|
|
||||||
out:
|
clock = wrap_max(clock, min_clock);
|
||||||
if (unlikely(clock < min_clock))
|
clock = wrap_min(clock, max_clock);
|
||||||
clock = min_clock;
|
|
||||||
|
|
||||||
scd->tick_jiffies = now_jiffies;
|
|
||||||
scd->clock = clock;
|
scd->clock = clock;
|
||||||
|
|
||||||
return clock;
|
return scd->clock;
|
||||||
}
|
}
|
||||||
|
|
||||||
static void lock_double_clock(struct sched_clock_data *data1,
|
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
|
* larger time as the latest time for both
|
||||||
* runqueues. (this creates monotonic movement)
|
* runqueues. (this creates monotonic movement)
|
||||||
*/
|
*/
|
||||||
if (likely(remote_clock < this_clock)) {
|
if (likely((s64)(remote_clock - this_clock) < 0)) {
|
||||||
clock = this_clock;
|
clock = this_clock;
|
||||||
scd->clock = clock;
|
scd->clock = clock;
|
||||||
} else {
|
} else {
|
||||||
|
@ -207,14 +207,9 @@ void sched_clock_tick(void)
|
||||||
now = sched_clock();
|
now = sched_clock();
|
||||||
|
|
||||||
__raw_spin_lock(&scd->lock);
|
__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_raw = now;
|
||||||
scd->tick_gtod = now_gtod;
|
scd->tick_gtod = now_gtod;
|
||||||
|
__update_sched_clock(scd, now);
|
||||||
__raw_spin_unlock(&scd->lock);
|
__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)
|
void sched_clock_idle_wakeup_event(u64 delta_ns)
|
||||||
{
|
{
|
||||||
struct sched_clock_data *scd = this_scd();
|
sched_clock_tick();
|
||||||
|
|
||||||
/*
|
|
||||||
* 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);
|
|
||||||
|
|
||||||
touch_softlockup_watchdog();
|
touch_softlockup_watchdog();
|
||||||
}
|
}
|
||||||
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
|
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
|
||||||
|
|
Loading…
Reference in a new issue