perf_counter: frequency based adaptive irq_period

Instead of specifying the irq_period for a counter, provide a target interrupt
frequency and dynamically adapt the irq_period to match this frequency.

[ Impact: new perf-counter attribute/feature ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <20090515132018.646195868@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 51 insertions, 12 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 93f4a0e4b873..0ad1db4f3d65 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1046,6 +1046,38 @@ int perf_counter_task_enable(void)
         return 0;
 }
 
+void perf_adjust_freq(struct perf_counter_context *ctx)
+{
+        struct perf_counter *counter;
+        u64 irq_period;
+        u64 events, period;
+        s64 delta;
+
+        spin_lock(&ctx->lock);
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                if (counter->state != PERF_COUNTER_STATE_ACTIVE)
+                        continue;
+
+                if (!counter->hw_event.freq || !counter->hw_event.irq_freq)
+                        continue;
+
+                events = HZ * counter->hw.interrupts * counter->hw.irq_period;
+                period = div64_u64(events, counter->hw_event.irq_freq);
+
+                delta = (s64)(1 + period - counter->hw.irq_period);
+                delta >>= 1;
+
+                irq_period = counter->hw.irq_period + delta;
+
+                if (!irq_period)
+                        irq_period = 1;
+
+                counter->hw.irq_period = irq_period;
+                counter->hw.interrupts = 0;
+        }
+        spin_unlock(&ctx->lock);
+}
+
 /*
  * Round-robin a context's counters:
  */
@@ -1081,6 +1113,9 @@ void perf_counter_task_tick(struct task_struct *curr, int cpu)
         cpuctx = &per_cpu(perf_cpu_context, cpu);
         ctx = &curr->perf_counter_ctx;
 
+        perf_adjust_freq(&cpuctx->ctx);
+        perf_adjust_freq(ctx);
+
         perf_counter_cpu_sched_out(cpuctx);
         __perf_counter_task_sched_out(ctx);
 
@@ -2382,6 +2417,8 @@ int perf_counter_overflow(struct perf_counter *counter,
         int events = atomic_read(&counter->event_limit);
         int ret = 0;
 
+        counter->hw.interrupts++;
+
         /*
          * XXX event_limit might not quite work as expected on inherited
          * counters
@@ -2450,6 +2487,7 @@ static enum hrtimer_restart perf_swcounter_hrtimer(struct hrtimer *hrtimer)
         enum hrtimer_restart ret = HRTIMER_RESTART;
         struct perf_counter *counter;
         struct pt_regs *regs;
+        u64 period;
 
         counter = container_of(hrtimer, struct perf_counter, hw.hrtimer);
         counter->pmu->read(counter);
@@ -2468,7 +2506,8 @@ static enum hrtimer_restart perf_swcounter_hrtimer(struct hrtimer *hrtimer)
                         ret = HRTIMER_NORESTART;
         }
 
-        hrtimer_forward_now(hrtimer, ns_to_ktime(counter->hw.irq_period));
+        period = max_t(u64, 10000, counter->hw.irq_period);
+        hrtimer_forward_now(hrtimer, ns_to_ktime(period));
 
         return ret;
 }
@@ -2629,8 +2668,9 @@ static int cpu_clock_perf_counter_enable(struct perf_counter *counter)
         hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
         hwc->hrtimer.function = perf_swcounter_hrtimer;
         if (hwc->irq_period) {
+                u64 period = max_t(u64, 10000, hwc->irq_period);
                 __hrtimer_start_range_ns(&hwc->hrtimer,
-                                ns_to_ktime(hwc->irq_period), 0,
+                                ns_to_ktime(period), 0,
                                 HRTIMER_MODE_REL, 0);
         }
 
@@ -2679,8 +2719,9 @@ static int task_clock_perf_counter_enable(struct perf_counter *counter)
         hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
         hwc->hrtimer.function = perf_swcounter_hrtimer;
         if (hwc->irq_period) {
+                u64 period = max_t(u64, 10000, hwc->irq_period);
                 __hrtimer_start_range_ns(&hwc->hrtimer,
-                                ns_to_ktime(hwc->irq_period), 0,
+                                ns_to_ktime(period), 0,
                                 HRTIMER_MODE_REL, 0);
         }
 
@@ -2811,9 +2852,7 @@ static const struct pmu *tp_perf_counter_init(struct perf_counter *counter)
 
 static const struct pmu *sw_perf_counter_init(struct perf_counter *counter)
 {
-        struct perf_counter_hw_event *hw_event = &counter->hw_event;
         const struct pmu *pmu = NULL;
-        struct hw_perf_counter *hwc = &counter->hw;
 
         /*
          * Software counters (currently) can't in general distinguish
@@ -2826,8 +2865,6 @@ static const struct pmu *sw_perf_counter_init(struct perf_counter *counter)
         case PERF_COUNT_CPU_CLOCK:
                 pmu = &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:
                 /*
@@ -2839,8 +2876,6 @@ static const struct pmu *sw_perf_counter_init(struct perf_counter *counter)
                 else
                         pmu = &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:
@@ -2854,9 +2889,6 @@ static const struct pmu *sw_perf_counter_init(struct perf_counter *counter)
                 break;
         }
 
-        if (pmu)
-                hwc->irq_period = hw_event->irq_period;
-
         return pmu;
 }
 
@@ -2872,6 +2904,7 @@ perf_counter_alloc(struct perf_counter_hw_event *hw_event,
 {
         const struct pmu *pmu;
         struct perf_counter *counter;
+        struct hw_perf_counter *hwc;
         long err;
 
         counter = kzalloc(sizeof(*counter), gfpflags);
@@ -2907,6 +2940,12 @@ perf_counter_alloc(struct perf_counter_hw_event *hw_event,
 
         pmu = NULL;
 
+        hwc = &counter->hw;
+        if (hw_event->freq && hw_event->irq_freq)
+                hwc->irq_period = TICK_NSEC / hw_event->irq_freq;
+        else
+                hwc->irq_period = hw_event->irq_period;
+
         /*
          * we currently do not support PERF_RECORD_GROUP on inherited counters
          */