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sched clock: couple local and remote clocks 

When taking the time of a remote CPU, use the opportunity to
couple (sync) the clocks to each other. (in a monotonic way)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mike Galbraith <efault@gmx.de>
This commit is contained in:
Ingo Molnar 2008-07-30 10:22:07 +02:00
parent 56b906126d
commit 4a273f209c
1 changed files with 21 additions and 12 deletions
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33
kernel/sched_clock.c
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@ -149,7 +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;
@ -158,26 +158,36 @@ 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 += scd->tick_raw - my_scd->tick_raw;
now += my_scd->tick_gtod - scd->tick_gtod;
this_clock = __update_sched_clock(my_scd, now);
remote_clock = scd->clock;
/*
* 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(remote_clock < this_clock)) {
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);
}
clock = __update_sched_clock(scd, now);
__raw_spin_unlock(&scd->lock);
return clock;
@ -223,7 +233,6 @@ 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