Commit 6c594c21 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

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: default avatarIngo Molnar <mingo@elte.hu>
parent 5d6a27d8

include/linux/perf_counter.h

+5 −3
Original line number Diff line number Diff line
@@ -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,

};



/*

include/linux/sched.h

+2 −1
Original line number Diff line number Diff line
@@ -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;

kernel/perf_counter.c

+49 −0
Original line number Diff line number Diff line
@@ -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;

	}

kernel/sched.c

+5 −2
Original line number Diff line number Diff line
@@ -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;