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:
Peter Zijlstra
Ingo Molnar
parent
efc2dead2c
commit
354879bb97
1 changed files with 34 additions and 50 deletions
|
|
@ -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;
|
||||
|
|
@ -91,47 +86,52 @@ void sched_clock_init(void)
|
|||
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
|
||||
*
|
||||
* - 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);
|
||||
|
|
|
|||
Loading…
Reference in a new issue