[PATCH v3 08/10] perf: cache perf_event_groups_first for cgroups

[Ian Rogers]

Add a per-CPU cache of the pinned and flexible perf_event_groups_first
value for a cgroup avoiding an O(log(#perf events)) searches during
sched_in.

Based-on-work-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 include/linux/perf_event.h |  6 +++
 kernel/events/core.c       | 79 +++++++++++++++++++++++++++-----------
 2 files changed, 62 insertions(+), 23 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index b3580afbf358..cfd0b320418c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -877,6 +877,12 @@ struct perf_cgroup_info {
 struct perf_cgroup {
 	struct cgroup_subsys_state	css;
 	struct perf_cgroup_info	__percpu *info;
+	/* A cache of the first event with the perf_cpu_context's
+	 * perf_event_context for the first event in pinned_groups or
+	 * flexible_groups. Avoids an rbtree search during sched_in.
+	 */
+	struct perf_event * __percpu    *pinned_event;
+	struct perf_event * __percpu    *flexible_event;
 };
 
 /*
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 11594d8bbb2e..9f0febf51d97 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1638,6 +1638,25 @@ perf_event_groups_insert(struct perf_event_groups *groups,
 
 	rb_link_node(&event->group_node, parent, node);
 	rb_insert_color(&event->group_node, &groups->tree);
+#ifdef CONFIG_CGROUP_PERF
+	if (is_cgroup_event(event)) {
+		struct perf_event **cgrp_event;
+
+		if (event->attr.pinned)
+			cgrp_event = per_cpu_ptr(event->cgrp->pinned_event,
+						event->cpu);
+		else
+			cgrp_event = per_cpu_ptr(event->cgrp->flexible_event,
+						event->cpu);
+		/*
+		 * Cgroup events for the same cgroup on the same CPU will
+		 * always be inserted at the right because of bigger
+		 * @groups->index. Only need to set *cgrp_event when it's NULL.
+		 */
+		if (!*cgrp_event)
+			*cgrp_event = event;
+	}
+#endif
 }
 
 /*
@@ -1652,6 +1671,9 @@ add_event_to_groups(struct perf_event *event, struct perf_event_context *ctx)
 	perf_event_groups_insert(groups, event);
 }
 
+static struct perf_event *
+perf_event_groups_next(struct perf_event *event);
+
 /*
  * Delete a group from a tree.
  */
@@ -1662,6 +1684,22 @@ perf_event_groups_delete(struct perf_event_groups *groups,
 	WARN_ON_ONCE(RB_EMPTY_NODE(&event->group_node) ||
 		     RB_EMPTY_ROOT(&groups->tree));
 
+#ifdef CONFIG_CGROUP_PERF
+	if (is_cgroup_event(event)) {
+		struct perf_event **cgrp_event;
+
+		if (event->attr.pinned)
+			cgrp_event = per_cpu_ptr(event->cgrp->pinned_event,
+						event->cpu);
+		else
+			cgrp_event = per_cpu_ptr(event->cgrp->flexible_event,
+						event->cpu);
+
+		if (*cgrp_event == event)
+			*cgrp_event = perf_event_groups_next(event);
+	}
+#endif
+
 	rb_erase(&event->group_node, &groups->tree);
 	init_event_group(event);
 }
@@ -1679,20 +1717,14 @@ del_event_from_groups(struct perf_event *event, struct perf_event_context *ctx)
 }
 
 /*
- * Get the leftmost event in the cpu/cgroup subtree.
+ * Get the leftmost event in the cpu subtree without a cgroup (ie task or
+ * system-wide).
  */
 static struct perf_event *
-perf_event_groups_first(struct perf_event_groups *groups, int cpu,
-			struct cgroup *cgrp)
+perf_event_groups_first_no_cgroup(struct perf_event_groups *groups, int cpu)
 {
 	struct perf_event *node_event = NULL, *match = NULL;
 	struct rb_node *node = groups->tree.rb_node;
-#ifdef CONFIG_CGROUP_PERF
-	int node_cgrp_id, cgrp_id = 0;
-
-	if (cgrp)
-		cgrp_id = cgrp->id;
-#endif
 
 	while (node) {
 		node_event = container_of(node, struct perf_event, group_node);
@@ -1706,18 +1738,10 @@ perf_event_groups_first(struct perf_event_groups *groups, int cpu,
 			continue;
 		}
 #ifdef CONFIG_CGROUP_PERF
-		node_cgrp_id = 0;
-		if (node_event->cgrp && node_event->cgrp->css.cgroup)
-			node_cgrp_id = node_event->cgrp->css.cgroup->id;
-
-		if (cgrp_id < node_cgrp_id) {
+		if (node_event->cgrp) {
 			node = node->rb_left;
 			continue;
 		}
-		if (cgrp_id > node_cgrp_id) {
-			node = node->rb_right;
-			continue;
-		}
 #endif
 		match = node_event;
 		node = node->rb_left;
@@ -3556,18 +3580,27 @@ static int ctx_groups_sched_in(struct perf_event_context *ctx,
 			.cap = ARRAY_SIZE(itrs),
 		};
 		/* Events not within a CPU context may be on any CPU. */
-		__heap_add(&event_heap, perf_event_groups_first(groups, -1,
-									NULL));
+		__heap_add(&event_heap,
+			perf_event_groups_first_no_cgroup(groups, -1));
 
 	}
 	evt = event_heap.data;
 
-	__heap_add(&event_heap, perf_event_groups_first(groups, cpu, NULL));
+	__heap_add(&event_heap,
+		perf_event_groups_first_no_cgroup(groups, cpu));
 
 #ifdef CONFIG_CGROUP_PERF
 	for (; css; css = css->parent) {
-		__heap_add(&event_heap, perf_event_groups_first(groups, cpu,
-								css->cgroup));
+		struct perf_cgroup *cgrp;
+
+		/* root cgroup doesn't have events */
+		if (css->id == 1)
+			break;
+
+		cgrp = container_of(css, struct perf_cgroup, css);
+		__heap_add(&event_heap, is_pinned
+			? *per_cpu_ptr(cgrp->pinned_event, cpu)
+			: *per_cpu_ptr(cgrp->flexible_event, cpu));
 	}
 #endif
 
-- 
2.24.0.432.g9d3f5f5b63-goog