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SubjectRe: [RFC][PATCH] perf: Rewrite enabled/running timekeeping
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On 05.09.2017 19:03, Peter Zijlstra wrote:
> On Tue, Sep 05, 2017 at 03:06:26PM +0300, Alexey Budankov wrote:
>> [ 6614.226305] WARNING: CPU: 45 PID: 43385 at kernel/events/core.c:239 event_function+0xb3/0xe0
>
> I think I avoided that problem by not radically rewriting
> perf_event_read() but fixing it instead:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=perf/core&id=8ad650955ede95e4a6fd6afbda2a0b37d4af9c29
>
> Full tree at:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/core
>
>
> Very minimally tested so far, I'll continue tomorrow.
>

The patch set v9 on top of peterz/queue perf/core repository above:

---
include/linux/perf_event.h | 16 ++-
kernel/events/core.c | 307 +++++++++++++++++++++++++++++++++++++--------
2 files changed, 267 insertions(+), 56 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2a6ae48..92cda40 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -557,7 +557,11 @@ struct perf_event {
*/
struct list_head group_entry;
struct list_head sibling_list;
-
+ /*
+ * Node on the pinned or flexible tree located at the event context;
+ */
+ struct rb_node group_node;
+ u64 group_index;
/*
* We need storage to track the entries in perf_pmu_migrate_context; we
* cannot use the event_entry because of RCU and we want to keep the
@@ -689,6 +693,12 @@ struct perf_event {
#endif /* CONFIG_PERF_EVENTS */
};

+
+struct perf_event_groups {
+ struct rb_root tree;
+ u64 index;
+};
+
/**
* struct perf_event_context - event context structure
*
@@ -709,8 +719,8 @@ struct perf_event_context {
struct mutex mutex;

struct list_head active_ctx_list;
- struct list_head pinned_groups;
- struct list_head flexible_groups;
+ struct perf_event_groups pinned_groups;
+ struct perf_event_groups flexible_groups;
struct list_head event_list;
int nr_events;
int nr_active;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 56e9214..8158f1d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1454,8 +1454,21 @@ static enum event_type_t get_event_type(struct perf_event *event)
return event_type;
}

-static struct list_head *
-ctx_group_list(struct perf_event *event, struct perf_event_context *ctx)
+/*
+ * Helper function to initialize group leader event;
+ */
+void init_event_group(struct perf_event *event)
+{
+ RB_CLEAR_NODE(&event->group_node);
+ event->group_index = 0;
+}
+
+/*
+ * Extract pinned or flexible groups from the context
+ * based on event attrs bits;
+ */
+static struct perf_event_groups *
+get_event_groups(struct perf_event *event, struct perf_event_context *ctx)
{
if (event->attr.pinned)
return &ctx->pinned_groups;
@@ -1464,6 +1477,169 @@ static enum event_type_t get_event_type(struct perf_event *event)
}

/*
+ * Helper function to initializes perf event groups object;
+ */
+void perf_event_groups_init(struct perf_event_groups *groups)
+{
+ groups->tree = RB_ROOT;
+ groups->index = 0;
+}
+
+/*
+ * Compare function for event groups;
+ * Implements complex key that first sorts by CPU and then by
+ * virtual index which provides ordering when rotating
+ * groups for the same CPU;
+ */
+int perf_event_groups_less(struct perf_event *left, struct perf_event *right)
+{
+ if (left->cpu < right->cpu) {
+ return 1;
+ } else if (left->cpu > right->cpu) {
+ return 0;
+ } else {
+ if (left->group_index < right->group_index) {
+ return 1;
+ } else if(left->group_index > right->group_index) {
+ return 0;
+ } else {
+ return 0;
+ }
+ }
+}
+
+/*
+ * Insert a group into a tree using event->cpu as a key. If event->cpu node
+ * is already attached to the tree then the event is added to the attached
+ * group's group_list list.
+ */
+static void
+perf_event_groups_insert(struct perf_event_groups *groups,
+ struct perf_event *event)
+{
+ struct perf_event *node_event;
+ struct rb_node *parent;
+ struct rb_node **node;
+
+ event->group_index = ++groups->index;
+
+ node = &groups->tree.rb_node;
+ parent = *node;
+
+ while (*node) {
+ parent = *node;
+ node_event = container_of(*node,
+ struct perf_event, group_node);
+
+ if (perf_event_groups_less(event, node_event))
+ node = &parent->rb_left;
+ else
+ node = &parent->rb_right;
+ }
+
+ rb_link_node(&event->group_node, parent, node);
+ rb_insert_color(&event->group_node, &groups->tree);
+}
+
+/*
+ * Helper function to insert event into the pinned or
+ * flexible groups;
+ */
+static void
+add_event_to_groups(struct perf_event *event, struct perf_event_context *ctx)
+{
+ struct perf_event_groups *groups;
+
+ groups = get_event_groups(event, ctx);
+ perf_event_groups_insert(groups, event);
+}
+
+/*
+ * Delete a group from a tree. If the group is directly attached to the tree
+ * it also detaches all groups on the group's group_list list.
+ */
+static void
+perf_event_groups_delete(struct perf_event_groups *groups,
+ struct perf_event *event)
+{
+ if (!RB_EMPTY_NODE(&event->group_node) &&
+ !RB_EMPTY_ROOT(&groups->tree))
+ rb_erase(&event->group_node, &groups->tree);
+
+ init_event_group(event);
+}
+
+/*
+ * Helper function to delete event from its groups;
+ */
+static void
+del_event_from_groups(struct perf_event *event, struct perf_event_context *ctx)
+{
+ struct perf_event_groups *groups;
+
+ groups = get_event_groups(event, ctx);
+ perf_event_groups_delete(groups, event);
+}
+
+/*
+ * Get a group by a cpu key from groups tree with the least group_index;
+ */
+static struct perf_event *
+perf_event_groups_first(struct perf_event_groups *groups, int cpu)
+{
+ struct perf_event *node_event = NULL, *match = NULL;
+ struct rb_node *node = groups->tree.rb_node;
+
+ while (node) {
+ node_event = container_of(node,
+ struct perf_event, group_node);
+
+ if (cpu < node_event->cpu) {
+ node = node->rb_left;
+ } else if (cpu > node_event->cpu) {
+ node = node->rb_right;
+ } else {
+ match = node_event;
+ node = node->rb_left;
+ }
+ }
+
+ return match;
+}
+
+/*
+ * Find group list by a cpu key and rotate it.
+ */
+static void
+perf_event_groups_rotate(struct perf_event_groups *groups, int cpu)
+{
+ struct perf_event *event =
+ perf_event_groups_first(groups, cpu);
+
+ if (event) {
+ perf_event_groups_delete(groups, event);
+ perf_event_groups_insert(groups, event);
+ }
+}
+
+/*
+ * Iterate event groups thru the whole tree.
+ */
+#define perf_event_groups_for_each(event, groups, node) \
+ for (event = rb_entry_safe(rb_first(&((groups)->tree)), \
+ typeof(*event), node); event; \
+ event = rb_entry_safe(rb_next(&event->node), \
+ typeof(*event), node))
+/*
+ * Iterate event groups with cpu == key.
+ */
+#define perf_event_groups_for_each_cpu(event, key, groups, node) \
+ for (event = perf_event_groups_first(groups, key); \
+ event && event->cpu == key; \
+ event = rb_entry_safe(rb_next(&event->node), \
+ typeof(*event), node))
+
+/*
* Add a event from the lists for its context.
* Must be called with ctx->mutex and ctx->lock held.
*/
@@ -1483,12 +1659,8 @@ static enum event_type_t get_event_type(struct perf_event *event)
* perf_group_detach can, at all times, locate all siblings.
*/
if (event->group_leader == event) {
- struct list_head *list;
-
event->group_caps = event->event_caps;
-
- list = ctx_group_list(event, ctx);
- list_add_tail(&event->group_entry, list);
+ add_event_to_groups(event, ctx);
}

list_update_cgroup_event(event, ctx, true);
@@ -1682,7 +1854,7 @@ static void perf_group_attach(struct perf_event *event)
list_del_rcu(&event->event_entry);

if (event->group_leader == event)
- list_del_init(&event->group_entry);
+ del_event_from_groups(event, ctx);

/*
* If event was in error state, then keep it
@@ -1700,7 +1872,6 @@ static void perf_group_attach(struct perf_event *event)
static void perf_group_detach(struct perf_event *event)
{
struct perf_event *sibling, *tmp;
- struct list_head *list = NULL;

lockdep_assert_held(&event->ctx->lock);

@@ -1721,22 +1892,23 @@ static void perf_group_detach(struct perf_event *event)
goto out;
}

- if (!list_empty(&event->group_entry))
- list = &event->group_entry;
-
/*
* If this was a group event with sibling events then
* upgrade the siblings to singleton events by adding them
* to whatever list we are on.
*/
list_for_each_entry_safe(sibling, tmp, &event->sibling_list, group_entry) {
- if (list)
- list_move_tail(&sibling->group_entry, list);
+
sibling->group_leader = sibling;

/* Inherit group flags from the previous leader */
sibling->group_caps = event->group_caps;

+ if (!RB_EMPTY_NODE(&event->group_node)) {
+ list_del_init(&sibling->group_entry);
+ add_event_to_groups(sibling, event->ctx);
+ }
+
WARN_ON_ONCE(sibling->ctx != event->ctx);
}

@@ -2180,6 +2352,22 @@ static int group_can_go_on(struct perf_event *event,
return can_add_hw;
}

+static int
+flexible_group_sched_in(struct perf_event *event,
+ struct perf_event_context *ctx,
+ struct perf_cpu_context *cpuctx,
+ int *can_add_hw)
+{
+ if (event->state <= PERF_EVENT_STATE_OFF || !event_filter_match(event))
+ return 0;
+
+ if (group_can_go_on(event, cpuctx, *can_add_hw))
+ if (group_sched_in(event, cpuctx, ctx))
+ *can_add_hw = 0;
+
+ return 1;
+}
+
static void add_event_to_ctx(struct perf_event *event,
struct perf_event_context *ctx)
{
@@ -2646,6 +2834,7 @@ static void ctx_sched_out(struct perf_event_context *ctx,
struct perf_cpu_context *cpuctx,
enum event_type_t event_type)
{
+ int sw = -1, cpu = smp_processor_id();
int is_active = ctx->is_active;
struct perf_event *event;

@@ -2694,12 +2883,20 @@ static void ctx_sched_out(struct perf_event_context *ctx,

perf_pmu_disable(ctx->pmu);
if (is_active & EVENT_PINNED) {
- list_for_each_entry(event, &ctx->pinned_groups, group_entry)
+ perf_event_groups_for_each_cpu(event, cpu,
+ &ctx->pinned_groups, group_node)
+ group_sched_out(event, cpuctx, ctx);
+ perf_event_groups_for_each_cpu(event, sw,
+ &ctx->pinned_groups, group_node)
group_sched_out(event, cpuctx, ctx);
}

if (is_active & EVENT_FLEXIBLE) {
- list_for_each_entry(event, &ctx->flexible_groups, group_entry)
+ perf_event_groups_for_each_cpu(event, cpu,
+ &ctx->flexible_groups, group_node)
+ group_sched_out(event, cpuctx, ctx);
+ perf_event_groups_for_each_cpu(event, sw,
+ &ctx->flexible_groups, group_node)
group_sched_out(event, cpuctx, ctx);
}
perf_pmu_enable(ctx->pmu);
@@ -2990,23 +3187,28 @@ static void cpu_ctx_sched_out(struct perf_cpu_context *cpuctx,
ctx_pinned_sched_in(struct perf_event_context *ctx,
struct perf_cpu_context *cpuctx)
{
+ int sw = -1, cpu = smp_processor_id();
struct perf_event *event;
+ int can_add_hw;
+
+ perf_event_groups_for_each_cpu(event, sw,
+ &ctx->pinned_groups, group_node) {
+ can_add_hw = 1;
+ if (flexible_group_sched_in(event, ctx, cpuctx, &can_add_hw)) {
+ if (event->state == PERF_EVENT_STATE_INACTIVE)
+ perf_event_set_state(event,
+ PERF_EVENT_STATE_ERROR);
+ }
+ }

- list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
- if (event->state <= PERF_EVENT_STATE_OFF)
- continue;
- if (!event_filter_match(event))
- continue;
-
- if (group_can_go_on(event, cpuctx, 1))
- group_sched_in(event, cpuctx, ctx);
-
- /*
- * If this pinned group hasn't been scheduled,
- * put it in error state.
- */
- if (event->state == PERF_EVENT_STATE_INACTIVE)
- perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
+ perf_event_groups_for_each_cpu(event, cpu,
+ &ctx->pinned_groups, group_node) {
+ can_add_hw = 1;
+ if (flexible_group_sched_in(event, ctx, cpuctx, &can_add_hw)) {
+ if (event->state == PERF_EVENT_STATE_INACTIVE)
+ perf_event_set_state(event,
+ PERF_EVENT_STATE_ERROR);
+ }
}
}

@@ -3014,25 +3216,19 @@ static void cpu_ctx_sched_out(struct perf_cpu_context *cpuctx,
ctx_flexible_sched_in(struct perf_event_context *ctx,
struct perf_cpu_context *cpuctx)
{
+ int sw = -1, cpu = smp_processor_id();
struct perf_event *event;
int can_add_hw = 1;

- list_for_each_entry(event, &ctx->flexible_groups, group_entry) {
- /* Ignore events in OFF or ERROR state */
- if (event->state <= PERF_EVENT_STATE_OFF)
- continue;
- /*
- * Listen to the 'cpu' scheduling filter constraint
- * of events:
- */
- if (!event_filter_match(event))
- continue;
+ perf_event_groups_for_each_cpu(event, sw,
+ &ctx->flexible_groups, group_node)
+ flexible_group_sched_in(event, ctx, cpuctx, &can_add_hw);
+
+ can_add_hw = 1;
+ perf_event_groups_for_each_cpu(event, cpu,
+ &ctx->flexible_groups, group_node)
+ flexible_group_sched_in(event, ctx, cpuctx, &can_add_hw);

- if (group_can_go_on(event, cpuctx, can_add_hw)) {
- if (group_sched_in(event, cpuctx, ctx))
- can_add_hw = 0;
- }
- }
}

static void
@@ -3113,7 +3309,7 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
* However, if task's ctx is not carrying any pinned
* events, no need to flip the cpuctx's events around.
*/
- if (!list_empty(&ctx->pinned_groups))
+ if (!RB_EMPTY_ROOT(&ctx->pinned_groups.tree))
cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
perf_event_sched_in(cpuctx, ctx, task);
perf_pmu_enable(ctx->pmu);
@@ -3350,8 +3546,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
* Rotate the first entry last of non-pinned groups. Rotation might be
* disabled by the inheritance code.
*/
- if (!ctx->rotate_disable)
- list_rotate_left(&ctx->flexible_groups);
+ if (!ctx->rotate_disable) {
+ int sw = -1, cpu = smp_processor_id();
+
+ perf_event_groups_rotate(&ctx->flexible_groups, sw);
+ perf_event_groups_rotate(&ctx->flexible_groups, cpu);
+ }
}

static int perf_rotate_context(struct perf_cpu_context *cpuctx)
@@ -3698,8 +3898,8 @@ static void __perf_event_init_context(struct perf_event_context *ctx)
raw_spin_lock_init(&ctx->lock);
mutex_init(&ctx->mutex);
INIT_LIST_HEAD(&ctx->active_ctx_list);
- INIT_LIST_HEAD(&ctx->pinned_groups);
- INIT_LIST_HEAD(&ctx->flexible_groups);
+ perf_event_groups_init(&ctx->pinned_groups);
+ perf_event_groups_init(&ctx->flexible_groups);
INIT_LIST_HEAD(&ctx->event_list);
atomic_set(&ctx->refcount, 1);
}
@@ -9370,6 +9570,7 @@ static void account_event(struct perf_event *event)
INIT_LIST_HEAD(&event->group_entry);
INIT_LIST_HEAD(&event->event_entry);
INIT_LIST_HEAD(&event->sibling_list);
+ init_event_group(event);
INIT_LIST_HEAD(&event->rb_entry);
INIT_LIST_HEAD(&event->active_entry);
INIT_LIST_HEAD(&event->addr_filters.list);
@@ -10880,7 +11081,7 @@ static int perf_event_init_context(struct task_struct *child, int ctxn)
* We dont have to disable NMIs - we are only looking at
* the list, not manipulating it:
*/
- list_for_each_entry(event, &parent_ctx->pinned_groups, group_entry) {
+ perf_event_groups_for_each(event, &parent_ctx->pinned_groups, group_node) {
ret = inherit_task_group(event, parent, parent_ctx,
child, ctxn, &inherited_all);
if (ret)
@@ -10896,7 +11097,7 @@ static int perf_event_init_context(struct task_struct *child, int ctxn)
parent_ctx->rotate_disable = 1;
raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);

- list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
+ perf_event_groups_for_each(event, &parent_ctx->flexible_groups, group_node) {
ret = inherit_task_group(event, parent, parent_ctx,
child, ctxn, &inherited_all);
if (ret)
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