*
* Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
*
+ * Updates and enhancements:
+ * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
+ *
* Based on code by:
* Ingo Molnar <mingo@redhat.com>
* Guillaume Chazarain <guichaz@gmail.com>
*
* 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>
#include <linux/spinlock.h>
-#include <linux/ktime.h>
+#include <linux/hardirq.h>
#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/ktime.h>
+#include <linux/sched.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 - INITIAL_JIFFIES)
+ * (NSEC_PER_SEC / HZ);
+}
+static __read_mostly int sched_clock_running;
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+__read_mostly int sched_clock_stable;
struct sched_clock_data {
/*
*/
raw_spinlock_t lock;
- unsigned long tick_jiffies;
- u64 prev_raw;
u64 tick_raw;
u64 tick_gtod;
u64 clock;
-#ifdef CONFIG_NO_HZ
- int check_max;
-#endif
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
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;
-#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)
-{
- return scd->check_max;
-}
-#else
-static int check_max(struct sched_clock_data *scd)
+static inline u64 wrap_max(u64 x, u64 y)
{
- return 1;
+ return (s64)(x - y) > 0 ? x : y;
}
-#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)
+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());
-
- min_clock = scd->tick_gtod +
- (delta_jiffies ? delta_jiffies - 1 : 0) * TICK_NSEC;
-
- 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;
- if (unlikely(clock + delta > max_clock) && check_max(scd)) {
- 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 = wrap_max(scd->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->prev_raw = now;
scd->clock = clock;
+
+ return scd->clock;
}
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;
+ struct sched_clock_data *scd;
+
+ if (sched_clock_stable)
+ return sched_clock();
+
+ scd = cpu_sdc(cpu);
+
+ /*
+ * Normally this is not called in NMI context - but if it is,
+ * trying to do any locking here is totally lethal.
+ */
+ if (unlikely(in_nmi()))
+ return scd->clock;
if (unlikely(!sched_clock_running))
return 0ull;
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);
} else {
__raw_spin_lock(&scd->lock);
+ clock = __update_sched_clock(scd, now);
}
- __update_sched_clock(scd, now);
- clock = scd->clock;
-
__raw_spin_unlock(&scd->lock);
return clock;
void sched_clock_tick(void)
{
- struct sched_clock_data *scd = this_scd();
- unsigned long now_jiffies = jiffies;
+ struct sched_clock_data *scd;
u64 now, now_gtod;
+ if (sched_clock_stable)
+ return;
+
if (unlikely(!sched_clock_running))
return;
WARN_ON_ONCE(!irqs_disabled());
- now = sched_clock();
+ scd = this_scd();
now_gtod = ktime_to_ns(ktime_get());
+ 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_jiffies = now_jiffies;
scd->tick_raw = now;
scd->tick_gtod = now_gtod;
+ __update_sched_clock(scd, now);
__raw_spin_unlock(&scd->lock);
}
*/
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;
- __raw_spin_unlock(&scd->lock);
+ if (timekeeping_suspended)
+ return;
+ 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)
+{
+ sched_clock_running = 1;
+}
+
+u64 sched_clock_cpu(int cpu)
{
- return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
+ if (unlikely(!sched_clock_running))
+ return 0;
+
+ return sched_clock();
+}
+
+#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
+
+unsigned long long cpu_clock(int cpu)
+{
+ unsigned long long clock;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ clock = sched_clock_cpu(cpu);
+ local_irq_restore(flags);
+
+ return clock;
}
+EXPORT_SYMBOL_GPL(cpu_clock);
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff