perf_counter: hrtimer based sampling for software time events

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>

2 files changed, 100 insertions, 43 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 4b14a8e9dbf5..dfb4c7ce18b3 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -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;
@@ -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;
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 68950a3a52bf..f9330d5827cf 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -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));
         }
@@ -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;
@@ -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)
@@ -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;
@@ -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);
@@ -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();
@@ -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);
 }
 
@@ -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 = {
@@ -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.
@@ -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: