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>

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index d2a16563415fe88b68337ad017a9c94404167c10..f30486fc55d724a9ae9f1eccd22cee6340539cf2 100644 (file)
--- 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 4c530278391b72dc6232179ae7432dbefe70ce5e..2e15be8fc792e6ecbf286bd33b4b8338ca2a4714 100644 (file)
--- 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 09287091c5266ff1f8c7042bd98d572eb87e95fa..fb11e351e44e339a78353040a1be16ec6a3b66eb 100644 (file)
--- 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 5c3f4106314ee585fa7af0d33c1bb1933fc6c073..382cfdb5e38d87295694c4c40d77368a5c49d834 100644 (file)
--- 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;