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perf_counter: More aggressive frequency adjustment

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Also employ the overflow handler to adjust the frequency, this results
in a stable frequency in about 40~50 samples, instead of that many ticks.

This also means we can start sampling at a sample period of 1 without
running head-first into the throttle.

It relies on sched_clock() to accurately measure the time difference
between the overflow NMIs.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-06-10 13:40:57 +02:00 committed by Ingo Molnar
parent dc81081b2d
commit bd2b5b1284
3 changed files with 92 additions and 44 deletions
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5
arch/x86/kernel/cpu/perf_counter.c
View File

@ -696,10 +696,11 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
if (!attr->exclude_kernel)
hwc->config |= ARCH_PERFMON_EVENTSEL_OS;
if (!hwc->sample_period)
if (!hwc->sample_period) {
hwc->sample_period = x86_pmu.max_period;
atomic64_set(&hwc->period_left, hwc->sample_period);
}
atomic64_set(&hwc->period_left, hwc->sample_period);
counter->destroy = hw_perf_counter_destroy;
/*

1
include/linux/perf_counter.h
View File

@ -371,6 +371,7 @@ struct hw_perf_counter {
u64 freq_count;
u64 freq_interrupts;
u64 freq_stamp;
#endif
};

130
kernel/perf_counter.c
View File

@ -1184,13 +1184,33 @@ static void perf_counter_cpu_sched_in(struct perf_cpu_context *cpuctx, int cpu)
static void perf_log_throttle(struct perf_counter *counter, int enable);
static void perf_log_period(struct perf_counter *counter, u64 period);
static void perf_adjust_freq(struct perf_counter_context *ctx)
static void perf_adjust_period(struct perf_counter *counter, u64 events)
{
struct hw_perf_counter *hwc = &counter->hw;
u64 period, sample_period;
s64 delta;
events *= hwc->sample_period;
period = div64_u64(events, counter->attr.sample_freq);
delta = (s64)(period - hwc->sample_period);
delta = (delta + 7) / 8; /* low pass filter */
sample_period = hwc->sample_period + delta;
if (!sample_period)
sample_period = 1;
perf_log_period(counter, sample_period);
hwc->sample_period = sample_period;
}
static void perf_ctx_adjust_freq(struct perf_counter_context *ctx)
{
struct perf_counter *counter;
struct hw_perf_counter *hwc;
u64 interrupts, sample_period;
u64 events, period, freq;
s64 delta;
u64 interrupts, freq;
spin_lock(&ctx->lock);
list_for_each_entry(counter, &ctx->counter_list, list_entry) {
@ -1202,6 +1222,9 @@ static void perf_adjust_freq(struct perf_counter_context *ctx)
interrupts = hwc->interrupts;
hwc->interrupts = 0;
/*
* unthrottle counters on the tick
*/
if (interrupts == MAX_INTERRUPTS) {
perf_log_throttle(counter, 1);
counter->pmu->unthrottle(counter);
@ -1211,6 +1234,9 @@ static void perf_adjust_freq(struct perf_counter_context *ctx)
if (!counter->attr.freq || !counter->attr.sample_freq)
continue;
/*
* if the specified freq < HZ then we need to skip ticks
*/
if (counter->attr.sample_freq < HZ) {
freq = counter->attr.sample_freq;
@ -1226,20 +1252,20 @@ static void perf_adjust_freq(struct perf_counter_context *ctx)
} else
freq = HZ;
events = freq * interrupts * hwc->sample_period;
period = div64_u64(events, counter->attr.sample_freq);
perf_adjust_period(counter, freq * interrupts);
delta = (s64)(1 + period - hwc->sample_period);
delta >>= 1;
sample_period = hwc->sample_period + delta;
if (!sample_period)
sample_period = 1;
perf_log_period(counter, sample_period);
hwc->sample_period = sample_period;
/*
* In order to avoid being stalled by an (accidental) huge
* sample period, force reset the sample period if we didn't
* get any events in this freq period.
*/
if (!interrupts) {
perf_disable();
counter->pmu->disable(counter);
atomic_set(&hwc->period_left, 0);
counter->pmu->enable(counter);
perf_enable();
}
}
spin_unlock(&ctx->lock);
}
@ -1279,9 +1305,9 @@ void perf_counter_task_tick(struct task_struct *curr, int cpu)
cpuctx = &per_cpu(perf_cpu_context, cpu);
ctx = curr->perf_counter_ctxp;
perf_adjust_freq(&cpuctx->ctx);
perf_ctx_adjust_freq(&cpuctx->ctx);
if (ctx)
perf_adjust_freq(ctx);
perf_ctx_adjust_freq(ctx);
perf_counter_cpu_sched_out(cpuctx);
if (ctx)
@ -1647,10 +1673,10 @@ static int perf_counter_period(struct perf_counter *counter, u64 __user *arg)
counter->attr.sample_freq = value;
} else {
perf_log_period(counter, value);
counter->attr.sample_period = value;
counter->hw.sample_period = value;
perf_log_period(counter, value);
}
unlock:
spin_unlock_irq(&ctx->lock);
@ -2853,35 +2879,41 @@ void __perf_counter_mmap(struct vm_area_struct *vma)
* event flow.
*/
struct freq_event {
struct perf_event_header header;
u64 time;
u64 id;
u64 period;
};
static void perf_log_period(struct perf_counter *counter, u64 period)
{
struct perf_output_handle handle;
struct freq_event event;
int ret;
struct {
struct perf_event_header header;
u64 time;
u64 id;
u64 period;
} freq_event = {
if (counter->hw.sample_period == period)
return;
if (counter->attr.sample_type & PERF_SAMPLE_PERIOD)
return;
event = (struct freq_event) {
.header = {
.type = PERF_EVENT_PERIOD,
.misc = 0,
.size = sizeof(freq_event),
.size = sizeof(event),
},
.time = sched_clock(),
.id = counter->id,
.period = period,
};
if (counter->hw.sample_period == period)
return;
ret = perf_output_begin(&handle, counter, sizeof(freq_event), 0, 0);
ret = perf_output_begin(&handle, counter, sizeof(event), 1, 0);
if (ret)
return;
perf_output_put(&handle, freq_event);
perf_output_put(&handle, event);
perf_output_end(&handle);
}
@ -2923,15 +2955,16 @@ int perf_counter_overflow(struct perf_counter *counter,
{
int events = atomic_read(&counter->event_limit);
int throttle = counter->pmu->unthrottle != NULL;
struct hw_perf_counter *hwc = &counter->hw;
int ret = 0;
if (!throttle) {
counter->hw.interrupts++;
hwc->interrupts++;
} else {
if (counter->hw.interrupts != MAX_INTERRUPTS) {
counter->hw.interrupts++;
if (HZ*counter->hw.interrupts > (u64)sysctl_perf_counter_limit) {
counter->hw.interrupts = MAX_INTERRUPTS;
if (hwc->interrupts != MAX_INTERRUPTS) {
hwc->interrupts++;
if (HZ * hwc->interrupts > (u64)sysctl_perf_counter_limit) {
hwc->interrupts = MAX_INTERRUPTS;
perf_log_throttle(counter, 0);
ret = 1;
}
@ -2945,6 +2978,16 @@ int perf_counter_overflow(struct perf_counter *counter,
}
}
if (counter->attr.freq) {
u64 now = sched_clock();
s64 delta = now - hwc->freq_stamp;
hwc->freq_stamp = now;
if (delta > 0 && delta < TICK_NSEC)
perf_adjust_period(counter, NSEC_PER_SEC / (int)delta);
}
/*
* XXX event_limit might not quite work as expected on inherited
* counters
@ -3379,7 +3422,6 @@ static const struct pmu *tp_perf_counter_init(struct perf_counter *counter)
return NULL;
counter->destroy = tp_perf_counter_destroy;
counter->hw.sample_period = counter->attr.sample_period;
return &perf_ops_generic;
}
@ -3483,10 +3525,11 @@ perf_counter_alloc(struct perf_counter_attr *attr,
pmu = NULL;
hwc = &counter->hw;
hwc->sample_period = attr->sample_period;
if (attr->freq && attr->sample_freq)
hwc->sample_period = div64_u64(TICK_NSEC, attr->sample_freq);
else
hwc->sample_period = attr->sample_period;
hwc->sample_period = 1;
atomic64_set(&hwc->period_left, hwc->sample_period);
/*
* we currently do not support PERF_SAMPLE_GROUP on inherited counters
@ -3687,6 +3730,9 @@ inherit_counter(struct perf_counter *parent_counter,
else
child_counter->state = PERF_COUNTER_STATE_OFF;
if (parent_counter->attr.freq)
child_counter->hw.sample_period = parent_counter->hw.sample_period;
/*
* Link it up in the child's context:
*/