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perf_counter: hrtimer based sampling for software time events
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Use hrtimers to profile timer based sampling for the software time
counters.

This allows platforms without hardware counter support to still
perform sample based profiling.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Peter Zijlstra authored and Ingo Molnar committed Apr 6, 2009
1 parent ac17dc8 commit d6d020e
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Showing 2 changed files with 100 additions and 43 deletions.
20 changes: 14 additions & 6 deletions include/linux/perf_counter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -114,6 +114,7 @@ struct perf_counter_hw_event {
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/spinlock.h>
#include <linux/hrtimer.h>
#include <asm/atomic.h>

struct task_struct;
Expand All @@ -123,12 +124,19 @@ struct task_struct;
*/
struct hw_perf_counter {
#ifdef CONFIG_PERF_COUNTERS
u64 config;
unsigned long config_base;
unsigned long counter_base;
int nmi;
unsigned int idx;
atomic64_t count; /* software */
union {
struct { /* hardware */
u64 config;
unsigned long config_base;
unsigned long counter_base;
int nmi;
unsigned int idx;
};
union { /* software */
atomic64_t count;
struct hrtimer hrtimer;
};
};
atomic64_t prev_count;
u64 irq_period;
atomic64_t period_left;
Expand Down
123 changes: 86 additions & 37 deletions kernel/perf_counter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1395,7 +1395,7 @@ static void perf_swcounter_handle_group(struct perf_counter *sibling)
struct perf_counter *counter, *group_leader = sibling->group_leader;

list_for_each_entry(counter, &group_leader->sibling_list, list_entry) {
perf_swcounter_update(counter);
counter->hw_ops->read(counter);
perf_swcounter_store_irq(sibling, counter->hw_event.type);
perf_swcounter_store_irq(sibling, atomic64_read(&counter->count));
}
Expand All @@ -1404,8 +1404,6 @@ static void perf_swcounter_handle_group(struct perf_counter *sibling)
static void perf_swcounter_interrupt(struct perf_counter *counter,
int nmi, struct pt_regs *regs)
{
perf_swcounter_save_and_restart(counter);

switch (counter->hw_event.record_type) {
case PERF_RECORD_SIMPLE:
break;
Expand All @@ -1426,6 +1424,38 @@ static void perf_swcounter_interrupt(struct perf_counter *counter,
wake_up(&counter->waitq);
}

static enum hrtimer_restart perf_swcounter_hrtimer(struct hrtimer *hrtimer)
{
struct perf_counter *counter;
struct pt_regs *regs;

counter = container_of(hrtimer, struct perf_counter, hw.hrtimer);
counter->hw_ops->read(counter);

regs = get_irq_regs();
/*
* In case we exclude kernel IPs or are somehow not in interrupt
* context, provide the next best thing, the user IP.
*/
if ((counter->hw_event.exclude_kernel || !regs) &&
!counter->hw_event.exclude_user)
regs = task_pt_regs(current);

if (regs)
perf_swcounter_interrupt(counter, 0, regs);

hrtimer_forward_now(hrtimer, ns_to_ktime(counter->hw.irq_period));

return HRTIMER_RESTART;
}

static void perf_swcounter_overflow(struct perf_counter *counter,
int nmi, struct pt_regs *regs)
{
perf_swcounter_save_and_restart(counter);
perf_swcounter_interrupt(counter, nmi, regs);
}

static int perf_swcounter_match(struct perf_counter *counter,
enum hw_event_types event,
struct pt_regs *regs)
Expand All @@ -1448,13 +1478,20 @@ static int perf_swcounter_match(struct perf_counter *counter,
return 1;
}

static void perf_swcounter_add(struct perf_counter *counter, u64 nr,
int nmi, struct pt_regs *regs)
{
int neg = atomic64_add_negative(nr, &counter->hw.count);
if (counter->hw.irq_period && !neg)
perf_swcounter_overflow(counter, nmi, regs);
}

static void perf_swcounter_ctx_event(struct perf_counter_context *ctx,
enum hw_event_types event, u64 nr,
int nmi, struct pt_regs *regs)
{
struct perf_counter *counter;
unsigned long flags;
int neg;

if (list_empty(&ctx->counter_list))
return;
Expand All @@ -1465,11 +1502,8 @@ static void perf_swcounter_ctx_event(struct perf_counter_context *ctx,
* XXX: make counter_list RCU safe
*/
list_for_each_entry(counter, &ctx->counter_list, list_entry) {
if (perf_swcounter_match(counter, event, regs)) {
neg = atomic64_add_negative(nr, &counter->hw.count);
if (counter->hw.irq_period && !neg)
perf_swcounter_interrupt(counter, nmi, regs);
}
if (perf_swcounter_match(counter, event, regs))
perf_swcounter_add(counter, nr, nmi, regs);
}

spin_unlock_irqrestore(&ctx->lock, flags);
Expand Down Expand Up @@ -1513,14 +1547,6 @@ static const struct hw_perf_counter_ops perf_ops_generic = {
* Software counter: cpu wall time clock
*/

static int cpu_clock_perf_counter_enable(struct perf_counter *counter)
{
int cpu = raw_smp_processor_id();

atomic64_set(&counter->hw.prev_count, cpu_clock(cpu));
return 0;
}

static void cpu_clock_perf_counter_update(struct perf_counter *counter)
{
int cpu = raw_smp_processor_id();
Expand All @@ -1533,8 +1559,26 @@ static void cpu_clock_perf_counter_update(struct perf_counter *counter)
atomic64_add(now - prev, &counter->count);
}

static int cpu_clock_perf_counter_enable(struct perf_counter *counter)
{
struct hw_perf_counter *hwc = &counter->hw;
int cpu = raw_smp_processor_id();

atomic64_set(&hwc->prev_count, cpu_clock(cpu));
if (hwc->irq_period) {
hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
hwc->hrtimer.function = perf_swcounter_hrtimer;
__hrtimer_start_range_ns(&hwc->hrtimer,
ns_to_ktime(hwc->irq_period), 0,
HRTIMER_MODE_REL, 0);
}

return 0;
}

static void cpu_clock_perf_counter_disable(struct perf_counter *counter)
{
hrtimer_cancel(&counter->hw.hrtimer);
cpu_clock_perf_counter_update(counter);
}

Expand Down Expand Up @@ -1580,27 +1624,33 @@ static void task_clock_perf_counter_update(struct perf_counter *counter, u64 now
atomic64_add(delta, &counter->count);
}

static void task_clock_perf_counter_read(struct perf_counter *counter)
{
u64 now = task_clock_perf_counter_val(counter, 1);

task_clock_perf_counter_update(counter, now);
}

static int task_clock_perf_counter_enable(struct perf_counter *counter)
{
if (counter->prev_state <= PERF_COUNTER_STATE_OFF)
atomic64_set(&counter->hw.prev_count,
task_clock_perf_counter_val(counter, 0));
struct hw_perf_counter *hwc = &counter->hw;

atomic64_set(&hwc->prev_count, task_clock_perf_counter_val(counter, 0));
if (hwc->irq_period) {
hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
hwc->hrtimer.function = perf_swcounter_hrtimer;
__hrtimer_start_range_ns(&hwc->hrtimer,
ns_to_ktime(hwc->irq_period), 0,
HRTIMER_MODE_REL, 0);
}

return 0;
}

static void task_clock_perf_counter_disable(struct perf_counter *counter)
{
u64 now = task_clock_perf_counter_val(counter, 0);
hrtimer_cancel(&counter->hw.hrtimer);
task_clock_perf_counter_update(counter,
task_clock_perf_counter_val(counter, 0));
}

task_clock_perf_counter_update(counter, now);
static void task_clock_perf_counter_read(struct perf_counter *counter)
{
task_clock_perf_counter_update(counter,
task_clock_perf_counter_val(counter, 1));
}

static const struct hw_perf_counter_ops perf_ops_task_clock = {
Expand Down Expand Up @@ -1729,16 +1779,12 @@ sw_perf_counter_init(struct perf_counter *counter)
*/
switch (counter->hw_event.type) {
case PERF_COUNT_CPU_CLOCK:
if (!(counter->hw_event.exclude_user ||
counter->hw_event.exclude_kernel ||
counter->hw_event.exclude_hv))
hw_ops = &perf_ops_cpu_clock;
hw_ops = &perf_ops_cpu_clock;

if (hw_event->irq_period && hw_event->irq_period < 10000)
hw_event->irq_period = 10000;
break;
case PERF_COUNT_TASK_CLOCK:
if (counter->hw_event.exclude_user ||
counter->hw_event.exclude_kernel ||
counter->hw_event.exclude_hv)
break;
/*
* If the user instantiates this as a per-cpu counter,
* use the cpu_clock counter instead.
Expand All @@ -1747,6 +1793,9 @@ sw_perf_counter_init(struct perf_counter *counter)
hw_ops = &perf_ops_task_clock;
else
hw_ops = &perf_ops_cpu_clock;

if (hw_event->irq_period && hw_event->irq_period < 10000)
hw_event->irq_period = 10000;
break;
case PERF_COUNT_PAGE_FAULTS:
case PERF_COUNT_PAGE_FAULTS_MIN:
Expand Down

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