[4.19,50/58] perf/cgroups: Dont rotate events for cgroups unnecessarily

--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -747,6 +747,11 @@  struct perf_event_context {
 	int				nr_stat;
 	int				nr_freq;
 	int				rotate_disable;
+	/*
+	 * Set when nr_events != nr_active, except tolerant to events not
+	 * necessary to be active due to scheduling constraints, such as cgroups.
+	 */
+	int				rotate_necessary;
 	atomic_t			refcount;
 	struct task_struct		*task;
 
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2952,6 +2952,12 @@  static void ctx_sched_out(struct perf_ev
 	if (!ctx->nr_active || !(is_active & EVENT_ALL))
 		return;
 
+	/*
+	 * If we had been multiplexing, no rotations are necessary, now no events
+	 * are active.
+	 */
+	ctx->rotate_necessary = 0;
+
 	perf_pmu_disable(ctx->pmu);
 	if (is_active & EVENT_PINNED) {
 		list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list)
@@ -3319,10 +3325,13 @@  static int flexible_sched_in(struct perf
 		return 0;
 
 	if (group_can_go_on(event, sid->cpuctx, sid->can_add_hw)) {
-		if (!group_sched_in(event, sid->cpuctx, sid->ctx))
-			list_add_tail(&event->active_list, &sid->ctx->flexible_active);
-		else
+		int ret = group_sched_in(event, sid->cpuctx, sid->ctx);
+		if (ret) {
 			sid->can_add_hw = 0;
+			sid->ctx->rotate_necessary = 1;
+			return 0;
+		}
+		list_add_tail(&event->active_list, &sid->ctx->flexible_active);
 	}
 
 	return 0;
@@ -3690,24 +3699,17 @@  ctx_first_active(struct perf_event_conte
 static bool perf_rotate_context(struct perf_cpu_context *cpuctx)
 {
 	struct perf_event *cpu_event = NULL, *task_event = NULL;
-	bool cpu_rotate = false, task_rotate = false;
-	struct perf_event_context *ctx = NULL;
+	struct perf_event_context *task_ctx = NULL;
+	int cpu_rotate, task_rotate;
 
 	/*
 	 * Since we run this from IRQ context, nobody can install new
 	 * events, thus the event count values are stable.
 	 */
 
-	if (cpuctx->ctx.nr_events) {
-		if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
-			cpu_rotate = true;
-	}
-
-	ctx = cpuctx->task_ctx;
-	if (ctx && ctx->nr_events) {
-		if (ctx->nr_events != ctx->nr_active)
-			task_rotate = true;
-	}
+	cpu_rotate = cpuctx->ctx.rotate_necessary;
+	task_ctx = cpuctx->task_ctx;
+	task_rotate = task_ctx ? task_ctx->rotate_necessary : 0;
 
 	if (!(cpu_rotate || task_rotate))
 		return false;
@@ -3716,7 +3718,7 @@  static bool perf_rotate_context(struct p
 	perf_pmu_disable(cpuctx->ctx.pmu);
 
 	if (task_rotate)
-		task_event = ctx_first_active(ctx);
+		task_event = ctx_first_active(task_ctx);
 	if (cpu_rotate)
 		cpu_event = ctx_first_active(&cpuctx->ctx);
 
@@ -3724,17 +3726,17 @@  static bool perf_rotate_context(struct p
 	 * As per the order given at ctx_resched() first 'pop' task flexible
 	 * and then, if needed CPU flexible.
 	 */
-	if (task_event || (ctx && cpu_event))
-		ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE);
+	if (task_event || (task_ctx && cpu_event))
+		ctx_sched_out(task_ctx, cpuctx, EVENT_FLEXIBLE);
 	if (cpu_event)
 		cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
 
 	if (task_event)
-		rotate_ctx(ctx, task_event);
+		rotate_ctx(task_ctx, task_event);
 	if (cpu_event)
 		rotate_ctx(&cpuctx->ctx, cpu_event);
 
-	perf_event_sched_in(cpuctx, ctx, current);
+	perf_event_sched_in(cpuctx, task_ctx, current);
 
 	perf_pmu_enable(cpuctx->ctx.pmu);
 	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);