perfcounters: add task migrations counter

Impact: add new feature, new sw counter

Add a counter that counts the number of cross-CPU migrations a
task is suffering.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

4 files changed, 61 insertions, 6 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index d2a16563415f..f30486fc55d7 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -42,6 +42,8 @@ enum hw_event_types {
         PERF_COUNT_BRANCH_INSTRUCTIONS  =  4,
         PERF_COUNT_BRANCH_MISSES        =  5,
 
+        PERF_HW_EVENTS_MAX              =  6,
+
         /*
          * Special "software" counters provided by the kernel, even if
          * the hardware does not support performance counters. These
@@ -50,11 +52,11 @@ enum hw_event_types {
          */
         PERF_COUNT_CPU_CLOCK            = -1,
         PERF_COUNT_TASK_CLOCK           = -2,
-        /*
-         * Future software events:
-         */
         PERF_COUNT_PAGE_FAULTS          = -3,
         PERF_COUNT_CONTEXT_SWITCHES     = -4,
+        PERF_COUNT_CPU_MIGRATIONS       = -5,
+
+        PERF_SW_EVENTS_MIN              = -6,
 };
 
 /*
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4c530278391b..2e15be8fc792 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1014,6 +1014,8 @@ struct sched_entity {
         u64                     last_wakeup;
         u64                     avg_overlap;
 
+        u64                     nr_migrations;
+
 #ifdef CONFIG_SCHEDSTATS
         u64                     wait_start;
         u64                     wait_max;
@@ -1029,7 +1031,6 @@ struct sched_entity {
         u64                     exec_max;
         u64                     slice_max;
 
-        u64                     nr_migrations;
         u64                     nr_migrations_cold;
         u64                     nr_failed_migrations_affine;
         u64                     nr_failed_migrations_running;
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 09287091c526..fb11e351e44e 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -936,6 +936,52 @@ static const struct hw_perf_counter_ops perf_ops_context_switches = {
         .hw_perf_counter_read           = context_switches_perf_counter_read,
 };
 
+static inline u64 get_cpu_migrations(void)
+{
+        return current->se.nr_migrations;
+}
+
+static void cpu_migrations_perf_counter_update(struct perf_counter *counter)
+{
+        u64 prev, now;
+        s64 delta;
+
+        prev = atomic64_read(&counter->hw.prev_count);
+        now = get_cpu_migrations();
+
+        atomic64_set(&counter->hw.prev_count, now);
+
+        delta = now - prev;
+        if (WARN_ON_ONCE(delta < 0))
+                delta = 0;
+
+        atomic64_add(delta, &counter->count);
+}
+
+static void cpu_migrations_perf_counter_read(struct perf_counter *counter)
+{
+        cpu_migrations_perf_counter_update(counter);
+}
+
+static void cpu_migrations_perf_counter_enable(struct perf_counter *counter)
+{
+        /*
+         * se.nr_migrations is a per-task value already,
+         * so we dont have to clear it on switch-in.
+         */
+}
+
+static void cpu_migrations_perf_counter_disable(struct perf_counter *counter)
+{
+        cpu_migrations_perf_counter_update(counter);
+}
+
+static const struct hw_perf_counter_ops perf_ops_cpu_migrations = {
+        .hw_perf_counter_enable         = cpu_migrations_perf_counter_enable,
+        .hw_perf_counter_disable        = cpu_migrations_perf_counter_disable,
+        .hw_perf_counter_read           = cpu_migrations_perf_counter_read,
+};
+
 static const struct hw_perf_counter_ops *
 sw_perf_counter_init(struct perf_counter *counter)
 {
@@ -951,6 +997,9 @@ sw_perf_counter_init(struct perf_counter *counter)
         case PERF_COUNT_CONTEXT_SWITCHES:
                 hw_ops = &perf_ops_context_switches;
                 break;
+        case PERF_COUNT_CPU_MIGRATIONS:
+                hw_ops = &perf_ops_cpu_migrations;
+                break;
         default:
                 break;
         }
diff --git a/kernel/sched.c b/kernel/sched.c
index 5c3f4106314e..382cfdb5e38d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1852,12 +1852,14 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
                 p->se.sleep_start -= clock_offset;
         if (p->se.block_start)
                 p->se.block_start -= clock_offset;
+#endif
         if (old_cpu != new_cpu) {
-                schedstat_inc(p, se.nr_migrations);
+                p->se.nr_migrations++;
+#ifdef CONFIG_SCHEDSTATS
                 if (task_hot(p, old_rq->clock, NULL))
                         schedstat_inc(p, se.nr_forced2_migrations);
-        }
 #endif
+        }
         p->se.vruntime -= old_cfsrq->min_vruntime -
                                          new_cfsrq->min_vruntime;
 
@@ -2375,6 +2377,7 @@ static void __sched_fork(struct task_struct *p)
         p->se.exec_start                = 0;
         p->se.sum_exec_runtime          = 0;
         p->se.prev_sum_exec_runtime     = 0;
+        p->se.nr_migrations             = 0;
         p->se.last_wakeup               = 0;
         p->se.avg_overlap               = 0;