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sched_clock: Make it NMI safe

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Arjan complained about the suckyness of TSC on modern machines, and
asked if we could do something about that for PERF_SAMPLE_TIME.

Make cpu_clock() NMI safe by removing the spinlock and using
cmpxchg. This also makes it smaller and more robust.

Affects architectures that use HAVE_UNSTABLE_SCHED_CLOCK, i.e. IA64
and x86.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-09-18 20:14:01 +02:00 committed by Ingo Molnar
parent cf450a7355
commit def0a9b257
2 changed files with 56 additions and 75 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
kernel/perf_counter.c
View file

@ -2955,10 +2955,7 @@ void perf_prepare_sample(struct perf_event_header *header,
}
if (sample_type & PERF_SAMPLE_TIME) {
/*
* Maybe do better on x86 and provide cpu_clock_nmi()
*/
data->time = sched_clock();
data->time = perf_clock();
header->size += sizeof(data->time);
}
@ -3488,7 +3485,7 @@ static void perf_log_throttle(struct perf_counter *counter, int enable)
.misc = 0,
.size = sizeof(throttle_event),
},
.time = sched_clock(),
.time = perf_clock(),
.id = primary_counter_id(counter),
.stream_id = counter->id,
};
@ -3540,7 +3537,7 @@ static int __perf_counter_overflow(struct perf_counter *counter, int nmi,
}
if (counter->attr.freq) {
u64 now = sched_clock();
u64 now = perf_clock();
s64 delta = now - hwc->freq_stamp;
hwc->freq_stamp = now;

122
kernel/sched_clock.c
View file

@ -48,13 +48,6 @@ static __read_mostly int sched_clock_running;
__read_mostly int sched_clock_stable;
struct sched_clock_data {
/*
* Raw spinlock - this is a special case: this might be called
* from within instrumentation code so we dont want to do any
* instrumentation ourselves.
*/
raw_spinlock_t lock;
u64 tick_raw;
u64 tick_gtod;
u64 clock;
@ -80,7 +73,6 @@ void sched_clock_init(void)
for_each_possible_cpu(cpu) {
struct sched_clock_data *scd = cpu_sdc(cpu);
scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
scd->tick_raw = 0;
scd->tick_gtod = ktime_now;
scd->clock = ktime_now;
@ -109,14 +101,19 @@ static inline u64 wrap_max(u64 x, u64 y)
* - filter out backward motion
* - use the GTOD tick value to create a window to filter crazy TSC values
*/
static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
static u64 sched_clock_local(struct sched_clock_data *scd)
{
s64 delta = now - scd->tick_raw;
u64 clock, min_clock, max_clock;
u64 now, clock, old_clock, min_clock, max_clock;
s64 delta;
again:
now = sched_clock();
delta = now - scd->tick_raw;
if (unlikely(delta < 0))
delta = 0;
old_clock = scd->clock;
/*
* scd->clock = clamp(scd->tick_gtod + delta,
* max(scd->tick_gtod, scd->clock),
@ -124,84 +121,73 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
*/
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);
min_clock = wrap_max(scd->tick_gtod, old_clock);
max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
clock = wrap_max(clock, min_clock);
clock = wrap_min(clock, max_clock);
scd->clock = clock;
if (cmpxchg(&scd->clock, old_clock, clock) != old_clock)
goto again;
return scd->clock;
return clock;
}
static void lock_double_clock(struct sched_clock_data *data1,
struct sched_clock_data *data2)
static u64 sched_clock_remote(struct sched_clock_data *scd)
{
if (data1 < data2) {
__raw_spin_lock(&data1->lock);
__raw_spin_lock(&data2->lock);
struct sched_clock_data *my_scd = this_scd();
u64 this_clock, remote_clock;
u64 *ptr, old_val, val;
sched_clock_local(my_scd);
again:
this_clock = my_scd->clock;
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((s64)(remote_clock - this_clock) < 0)) {
ptr = &scd->clock;
old_val = remote_clock;
val = this_clock;
} else {
__raw_spin_lock(&data2->lock);
__raw_spin_lock(&data1->lock);
/*
* Should be rare, but possible:
*/
ptr = &my_scd->clock;
old_val = this_clock;
val = remote_clock;
}
if (cmpxchg(ptr, old_val, val) != old_val)
goto again;
return val;
}
u64 sched_clock_cpu(int cpu)
{
u64 now, clock, this_clock, remote_clock;
struct sched_clock_data *scd;
u64 clock;
WARN_ON_ONCE(!irqs_disabled());
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;
WARN_ON_ONCE(!irqs_disabled());
now = sched_clock();
scd = cpu_sdc(cpu);
if (cpu != raw_smp_processor_id()) {
struct sched_clock_data *my_scd = this_scd();
lock_double_clock(scd, my_scd);
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((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);
}
__raw_spin_unlock(&scd->lock);
if (cpu != smp_processor_id())
clock = sched_clock_remote(scd);
else
clock = sched_clock_local(scd);
return clock;
}
@ -223,11 +209,9 @@ void sched_clock_tick(void)
now_gtod = ktime_to_ns(ktime_get());
now = sched_clock();
__raw_spin_lock(&scd->lock);
scd->tick_raw = now;
scd->tick_gtod = now_gtod;
__update_sched_clock(scd, now);
__raw_spin_unlock(&scd->lock);
sched_clock_local(scd);
}
/*