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-rw-r--r--kernel/sched_clock.c224
1 files changed, 71 insertions, 153 deletions
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 22ed55d..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>
@@ -32,13 +30,19 @@
#include <linux/ktime.h>
#include <linux/module.h>
+/*
+ * Scheduler clock - returns current time in nanosec units.
+ * This is default implementation.
+ * Architectures and sub-architectures can override this.
+ */
+unsigned long long __attribute__((weak)) sched_clock(void)
+{
+ return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
+}
-#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+static __read_mostly int sched_clock_running;
-#define MULTI_SHIFT 15
-/* Max is double, Min is 1/2 */
-#define MAX_MULTI (2LL << MULTI_SHIFT)
-#define MIN_MULTI (1LL << (MULTI_SHIFT-1))
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
struct sched_clock_data {
/*
@@ -48,15 +52,9 @@ struct sched_clock_data {
*/
raw_spinlock_t lock;
- unsigned long tick_jiffies;
- u64 prev_raw;
u64 tick_raw;
u64 tick_gtod;
u64 clock;
- s64 multi;
-#ifdef CONFIG_NO_HZ
- int check_max;
-#endif
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
@@ -71,121 +69,69 @@ static inline struct sched_clock_data *cpu_sdc(int cpu)
return &per_cpu(sched_clock_data, cpu);
}
-static __read_mostly int sched_clock_running;
-
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->prev_raw = 0;
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
}
sched_clock_running = 1;
}
-#ifdef CONFIG_NO_HZ
/*
- * The dynamic ticks makes the delta jiffies inaccurate. This
- * prevents us from checking the maximum time update.
- * Disable the maximum check during stopped ticks.
+ * min,max except they take wrapping into account
*/
-void sched_clock_tick_stop(int cpu)
-{
- struct sched_clock_data *scd = cpu_sdc(cpu);
-
- scd->check_max = 0;
-}
-void sched_clock_tick_start(int cpu)
+static inline u64 wrap_min(u64 x, u64 y)
{
- struct sched_clock_data *scd = cpu_sdc(cpu);
-
- scd->check_max = 1;
+ return (s64)(x - y) < 0 ? x : y;
}
-static int check_max(struct sched_clock_data *scd)
+static inline u64 wrap_max(u64 x, u64 y)
{
- return scd->check_max;
+ return (s64)(x - y) > 0 ? x : y;
}
-#else
-static int check_max(struct sched_clock_data *scd)
-{
- return 1;
-}
-#endif /* CONFIG_NO_HZ */
/*
* 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 void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *time)
+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->prev_raw;
+ s64 delta = now - scd->tick_raw;
+ u64 clock, min_clock, max_clock;
WARN_ON_ONCE(!irqs_disabled());
- /*
- * 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++;
- goto out;
- }
+ if (unlikely(delta < 0))
+ delta = 0;
/*
- * The clock must stay within a jiffie of the gtod.
- * But since we may be at the start of a jiffy or the end of one
- * we add another jiffy buffer.
+ * scd->clock = clamp(scd->tick_gtod + delta,
+ * max(scd->tick_gtod, scd->clock),
+ * scd->tick_gtod + TICK_NSEC);
*/
- max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
- delta *= scd->multi;
- delta >>= MULTI_SHIFT;
+ clock = scd->tick_gtod + delta;
+ min_clock = wrap_max(scd->tick_gtod, scd->clock);
+ max_clock = scd->tick_gtod + TICK_NSEC;
- if (unlikely(clock + delta > max_clock) && check_max(scd)) {
- if (clock < max_clock)
- clock = max_clock;
- else
- clock++;
- } else {
- clock += delta;
- }
+ clock = wrap_max(clock, min_clock);
+ clock = wrap_min(clock, max_clock);
- out:
- if (unlikely(clock < min_clock))
- clock = min_clock;
+ scd->clock = clock;
- if (time)
- *time = clock;
- else {
- scd->prev_raw = now;
- scd->clock = clock;
- }
+ return scd->clock;
}
static void lock_double_clock(struct sched_clock_data *data1,
@@ -203,7 +149,7 @@ static void lock_double_clock(struct sched_clock_data *data1,
u64 sched_clock_cpu(int cpu)
{
struct sched_clock_data *scd = cpu_sdc(cpu);
- u64 now, clock;
+ u64 now, clock, this_clock, remote_clock;
if (unlikely(!sched_clock_running))
return 0ull;
@@ -212,43 +158,44 @@ u64 sched_clock_cpu(int cpu)
now = sched_clock();
if (cpu != raw_smp_processor_id()) {
- /*
- * in order to update a remote cpu's clock based on our
- * unstable raw time rebase it against:
- * tick_raw (offset between raw counters)
- * tick_gotd (tick offset between cpus)
- */
struct sched_clock_data *my_scd = this_scd();
lock_double_clock(scd, my_scd);
- now -= my_scd->tick_raw;
- now += scd->tick_raw;
+ this_clock = __update_sched_clock(my_scd, now);
+ remote_clock = scd->clock;
- now += my_scd->tick_gtod;
- now -= scd->tick_gtod;
+ /*
+ * Use the opportunity that we have both locks
+ * taken to couple the two clocks: we take the
+ * larger time as the latest time for both
+ * runqueues. (this creates monotonic movement)
+ */
+ if (likely((s64)(remote_clock - this_clock) < 0)) {
+ clock = this_clock;
+ scd->clock = clock;
+ } else {
+ /*
+ * Should be rare, but possible:
+ */
+ clock = remote_clock;
+ my_scd->clock = remote_clock;
+ }
__raw_spin_unlock(&my_scd->lock);
-
- __update_sched_clock(scd, now, &clock);
-
- __raw_spin_unlock(&scd->lock);
-
} else {
__raw_spin_lock(&scd->lock);
- __update_sched_clock(scd, now, NULL);
- clock = scd->clock;
- __raw_spin_unlock(&scd->lock);
+ clock = __update_sched_clock(scd, now);
}
+ __raw_spin_unlock(&scd->lock);
+
return clock;
}
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))
@@ -260,29 +207,9 @@ void sched_clock_tick(void)
now = sched_clock();
__raw_spin_lock(&scd->lock);
- __update_sched_clock(scd, now, NULL);
- /*
- * 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.
- */
- 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;
+ __update_sched_clock(scd, now);
__raw_spin_unlock(&scd->lock);
}
@@ -300,37 +227,28 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
*/
void sched_clock_idle_wakeup_event(u64 delta_ns)
{
- struct sched_clock_data *scd = this_scd();
- u64 now = sched_clock();
-
- /*
- * 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->prev_raw = now;
- scd->clock += delta_ns;
- scd->multi = 1 << MULTI_SHIFT;
- __raw_spin_unlock(&scd->lock);
-
+ sched_clock_tick();
touch_softlockup_watchdog();
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
-#endif
+#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
-/*
- * Scheduler clock - returns current time in nanosec units.
- * This is default implementation.
- * Architectures and sub-architectures can override this.
- */
-unsigned long long __attribute__((weak)) sched_clock(void)
+void sched_clock_init(void)
{
- return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
+ sched_clock_running = 1;
}
+u64 sched_clock_cpu(int cpu)
+{
+ if (unlikely(!sched_clock_running))
+ return 0;
+
+ return sched_clock();
+}
+
+#endif
+
unsigned long long cpu_clock(int cpu)
{
unsigned long long clock;
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