[PATCH 06/30] sched: sched_clock_cpu() based cpu_clock()

Peter Zijlstra
2008-06-27T12:07:51Z

[-- Attachment #1: sched-cpu_clock.patch --]
[-- Type: text/plain, Size: 3257 bytes --]

with sched_clock_cpu() being reasonably in sync between cpus (max 1 jiffy
difference) use this to provide cpu_clock().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/sched.c | 80 ---------------------------------------------------
kernel/sched_clock.c | 12 +++++++
2 files changed, 12 insertions(+), 80 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -809,82 +807,6 @@ static inline u64 global_rt_runtime(void
return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
}

-unsigned long long time_sync_thresh = 100000;
-
-static DEFINE_PER_CPU(unsigned long long, time_offset);
-static DEFINE_PER_CPU(unsigned long long, prev_cpu_time);
-
-/*
- * Global lock which we take every now and then to synchronize
- * the CPUs time. This method is not warp-safe, but it's good
- * enough to synchronize slowly diverging time sources and thus
- * it's good enough for tracing:
- */
-static DEFINE_SPINLOCK(time_sync_lock);
-static unsigned long long prev_global_time;
-
-static unsigned long long __sync_cpu_clock(unsigned long long time, int cpu)
-{
- /*
- * We want this inlined, to not get tracer function calls
- * in this critical section:
- */
- spin_acquire(&time_sync_lock.dep_map, 0, 0, _THIS_IP_);
- __raw_spin_lock(&time_sync_lock.raw_lock);
-
- if (time < prev_global_time) {
- per_cpu(time_offset, cpu) += prev_global_time - time;
- time = prev_global_time;
- } else {
- prev_global_time = time;
- }
-
- __raw_spin_unlock(&time_sync_lock.raw_lock);
- spin_release(&time_sync_lock.dep_map, 1, _THIS_IP_);
-
- return time;
-}
-
-static unsigned long long __cpu_clock(int cpu)
-{
- unsigned long long now;
-
- /*
- * Only call sched_clock() if the scheduler has already been
- * initialized (some code might call cpu_clock() very early):
- */
- if (unlikely(!scheduler_running))
- return 0;
-
- now = sched_clock_cpu(cpu);
-
- return now;
-}
-
-/*
- * For kernel-internal use: high-speed (but slightly incorrect) per-cpu
- * clock constructed from sched_clock():
- */
-unsigned long long cpu_clock(int cpu)
-{
- unsigned long long prev_cpu_time, time, delta_time;
- unsigned long flags;
-
- local_irq_save(flags);
- prev_cpu_time = per_cpu(prev_cpu_time, cpu);
- time = __cpu_clock(cpu) + per_cpu(time_offset, cpu);
- delta_time = time-prev_cpu_time;
-
- if (unlikely(delta_time > time_sync_thresh)) {
- time = __sync_cpu_clock(time, cpu);
- per_cpu(prev_cpu_time, cpu) = time;
- }
- local_irq_restore(flags);
-
- return time;
-}
-EXPORT_SYMBOL_GPL(cpu_clock);
-
#ifndef prepare_arch_switch
# define prepare_arch_switch(next) do { } while (0)
#endif
Index: linux-2.6/kernel/sched_clock.c
===================================================================
--- linux-2.6.orig/kernel/sched_clock.c
+++ linux-2.6/kernel/sched_clock.c
@@ -244,3 +244,15 @@ unsigned long long __attribute__((weak))
{
return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
}
+
+unsigned long long cpu_clock(int cpu)
+{
+ unsigned long long clock;
+ unsigned long flags;
+
+ raw_local_irq_save(flags);
+ clock = sched_clock_cpu(cpu);
+ raw_local_irq_restore(flags);
+
+ return clock;
+}

--