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sched: sched_clock_cpu() based cpu_clock()

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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>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2008-06-27 13:41:15 +02:00 committed by Ingo Molnar
parent c09595f63b
commit 76a2a6ee8a
2 changed files with 12 additions and 76 deletions
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76
kernel/sched.c
View file

@ -818,82 +818,6 @@ 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

12
kernel/sched_clock.c
View file

@ -244,3 +244,15 @@ unsigned long long __attribute__((weak)) sched_clock(void)
{
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;
}