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Subject[PATCH 3/3] perf_counter: generic per counter interrupt throttle
Introduce a generic per counter interrupt throttle.

This uses the perf_counter_overflow() quick disable to throttle a specific
counter when its going too fast when a pmu->unthrottle() method is provided
which can undo the quick disable.

Power needs to implement both the quick disable and the unthrottle method.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
arch/x86/kernel/cpu/perf_counter.c | 13 ++++++++
include/linux/perf_counter.h | 11 ++++++
kernel/perf_counter.c | 59 ++++++++++++++++++++++++++++++++++---
kernel/sysctl.c | 8 +++++
4 files changed, 87 insertions(+), 4 deletions(-)
Index: linux-2.6/include/linux/perf_counter.h
===================================================================
--- linux-2.6.orig/include/linux/perf_counter.h
+++ linux-2.6/include/linux/perf_counter.h
@@ -267,6 +267,15 @@ enum perf_event_type {
PERF_EVENT_PERIOD = 4,

/*
+ * struct {
+ * struct perf_event_header header;
+ * u64 time;
+ * };
+ */
+ PERF_EVENT_THROTTLE = 5,
+ PERF_EVENT_UNTHROTTLE = 6,
+
+ /*
* When header.misc & PERF_EVENT_MISC_OVERFLOW the event_type field
* will be PERF_RECORD_*
*
@@ -367,6 +376,7 @@ struct pmu {
int (*enable) (struct perf_counter *counter);
void (*disable) (struct perf_counter *counter);
void (*read) (struct perf_counter *counter);
+ void (*unthrottle) (struct perf_counter *counter);
};

/**
@@ -613,6 +623,7 @@ extern struct perf_callchain_entry *perf

extern int sysctl_perf_counter_priv;
extern int sysctl_perf_counter_mlock;
+extern int sysctl_perf_counter_limit;

extern void perf_counter_init(void);

Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -46,6 +46,7 @@ static atomic_t nr_comm_tracking __read_

int sysctl_perf_counter_priv __read_mostly; /* do we need to be privileged */
int sysctl_perf_counter_mlock __read_mostly = 512; /* 'free' kb per user */
+int sysctl_perf_counter_limit __read_mostly = 100000; /* max NMIs per second */

/*
* Lock for (sysadmin-configurable) counter reservations:
@@ -1091,12 +1092,15 @@ int perf_counter_task_disable(void)
return 0;
}

+#define MAX_INTERRUPTS (~0ULL)
+
+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)
{
struct perf_counter *counter;
- u64 irq_period;
+ u64 interrupts, irq_period;
u64 events, period;
s64 delta;

@@ -1105,10 +1109,19 @@ static void perf_adjust_freq(struct perf
if (counter->state != PERF_COUNTER_STATE_ACTIVE)
continue;

+ interrupts = counter->hw.interrupts;
+ counter->hw.interrupts = 0;
+
+ if (interrupts == MAX_INTERRUPTS) {
+ perf_log_throttle(counter, 1);
+ counter->pmu->unthrottle(counter);
+ interrupts = 2*sysctl_perf_counter_limit/HZ;
+ }
+
if (!counter->hw_event.freq || !counter->hw_event.irq_freq)
continue;

- events = HZ * counter->hw.interrupts * counter->hw.irq_period;
+ events = HZ * interrupts * counter->hw.irq_period;
period = div64_u64(events, counter->hw_event.irq_freq);

delta = (s64)(1 + period - counter->hw.irq_period);
@@ -1122,7 +1135,6 @@ static void perf_adjust_freq(struct perf
perf_log_period(counter, irq_period);

counter->hw.irq_period = irq_period;
- counter->hw.interrupts = 0;
}
spin_unlock(&ctx->lock);
}
@@ -2545,6 +2557,35 @@ static void perf_log_period(struct perf_
}

/*
+ * IRQ throttle logging
+ */
+
+static void perf_log_throttle(struct perf_counter *counter, int enable)
+{
+ struct perf_output_handle handle;
+ int ret;
+
+ struct {
+ struct perf_event_header header;
+ u64 time;
+ } throttle_event = {
+ .header = {
+ .type = PERF_EVENT_THROTTLE + 1,
+ .misc = 0,
+ .size = sizeof(throttle_event),
+ },
+ .time = sched_clock(),
+ };
+
+ ret = perf_output_begin(&handle, counter, sizeof(throttle_event), 0, 0);
+ if (ret)
+ return;
+
+ perf_output_put(&handle, throttle_event);
+ perf_output_end(&handle);
+}
+
+/*
* Generic counter overflow handling.
*/

@@ -2552,9 +2593,19 @@ int perf_counter_overflow(struct perf_co
int nmi, struct pt_regs *regs, u64 addr)
{
int events = atomic_read(&counter->event_limit);
+ int throttle = counter->pmu->unthrottle != NULL;
int ret = 0;

- counter->hw.interrupts++;
+ if (!throttle) {
+ counter->hw.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;
+ perf_log_throttle(counter, 0);
+ ret = 1;
+ }
+ }

/*
* XXX event_limit might not quite work as expected on inherited
Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c
+++ linux-2.6/kernel/sysctl.c
@@ -939,6 +939,14 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "perf_counter_int_limit",
+ .data = &sysctl_perf_counter_limit,
+ .maxlen = sizeof(sysctl_perf_counter_limit),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
#endif
/*
* NOTE: do not add new entries to this table unless you have read
Index: linux-2.6/arch/x86/kernel/cpu/perf_counter.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/perf_counter.c
+++ linux-2.6/arch/x86/kernel/cpu/perf_counter.c
@@ -623,6 +623,18 @@ try_generic:
return 0;
}

+static void x86_pmu_unthrottle(struct perf_counter *counter)
+{
+ struct cpu_hw_counters *cpuc = &__get_cpu_var(cpu_hw_counters);
+ struct hw_perf_counter *hwc = &counter->hw;
+
+ if (WARN_ON_ONCE(hwc->idx >= X86_PMC_IDX_MAX ||
+ cpuc->counters[hwc->idx] != counter))
+ return;
+
+ x86_pmu.enable(hwc, hwc->idx);
+}
+
void perf_counter_print_debug(void)
{
u64 ctrl, status, overflow, pmc_ctrl, pmc_count, prev_left, fixed;
@@ -1038,6 +1050,7 @@ static const struct pmu pmu = {
.enable = x86_pmu_enable,
.disable = x86_pmu_disable,
.read = x86_pmu_read,
+ .unthrottle = x86_pmu_unthrottle,
};

const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
--



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