Commit 5d6a27d8 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

perfcounters: add context switch counter 



Impact: add new feature, new sw counter

Add a counter that counts the number of context-switches a task
is doing.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 8cb391e8

include/linux/perf_counter.h

+2 −2
Original line number Diff line number Diff line
@@ -53,8 +53,8 @@ enum hw_event_types { 
	/*

	 * Future software events:

	 */

	/* PERF_COUNT_PAGE_FAULTS	= -3,

	   PERF_COUNT_CONTEXT_SWITCHES	= -4, */

	PERF_COUNT_PAGE_FAULTS		= -3,

	PERF_COUNT_CONTEXT_SWITCHES	= -4,

};



/*

kernel/perf_counter.c

+51 −0
Original line number Diff line number Diff line
@@ -888,6 +888,54 @@ static const struct hw_perf_counter_ops perf_ops_task_clock = { 
	.hw_perf_counter_read		= task_clock_perf_counter_read,

};



static u64 get_context_switches(void)

{

	struct task_struct *curr = current;



	return curr->nvcsw + curr->nivcsw;

}



static void context_switches_perf_counter_update(struct perf_counter *counter)

{

	u64 prev, now;

	s64 delta;



	prev = atomic64_read(&counter->hw.prev_count);

	now = get_context_switches();



	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 context_switches_perf_counter_read(struct perf_counter *counter)

{

	context_switches_perf_counter_update(counter);

}



static void context_switches_perf_counter_enable(struct perf_counter *counter)

{

	/*

	 * ->nvcsw + curr->nivcsw is a per-task value already,

	 * so we dont have to clear it on switch-in.

	 */

}



static void context_switches_perf_counter_disable(struct perf_counter *counter)

{

	context_switches_perf_counter_update(counter);

}



static const struct hw_perf_counter_ops perf_ops_context_switches = {

	.hw_perf_counter_enable		= context_switches_perf_counter_enable,

	.hw_perf_counter_disable	= context_switches_perf_counter_disable,

	.hw_perf_counter_read		= context_switches_perf_counter_read,

};



static const struct hw_perf_counter_ops *

sw_perf_counter_init(struct perf_counter *counter)

{
@@ -900,6 +948,9 @@ sw_perf_counter_init(struct perf_counter *counter) 
	case PERF_COUNT_TASK_CLOCK:

		hw_ops = &perf_ops_task_clock;

		break;

	case PERF_COUNT_CONTEXT_SWITCHES:

		hw_ops = &perf_ops_context_switches;

		break;

	default:

		break;

	}