perf: De-schedule a task context when removing the last event

Since perf_install_in_context() will now install a context when we
add the first event, we can de-schedule the context when the last
event is removed.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110409192142.090431763@chello.nlSigned-off-by: Ingo Molnar <mingo@elte.hu>

kernel/events/core.c

@@ -1120,6 +1120,10 @@ static int __perf_remove_from_context(void *info)
 	raw_spin_lock(&ctx->lock);
 	event_sched_out(event, cpuctx, ctx);
 	list_del_event(event, ctx);
+	if (!ctx->nr_events && cpuctx->task_ctx == ctx) {
+		ctx->is_active = 0;
+		cpuctx->task_ctx = NULL;
+	}
 	raw_spin_unlock(&ctx->lock);
 
 	return 0;