[PATCH] perf: update perf_cgroup time for ancestor cgroup(s)

[Song Liu]

When a perf_event is attached to parent cgroup, it should count events
for all children cgroups:

 parent_group   <---- perf_event
   \
    - child_group  <---- process(es)

However, in our tests, we found this perf_event cannot report reliable
results. This is because perf_event->cgrp and cpuctx->cgrp are not
identical, thus perf_event->cgrp are not updated properly.

This patch fixes this by updating perf_cgroup properly for ancestor
cgroup(s).

Signed-off-by: Song Liu <songliubrav...@fb.com>
Reported-by: Ephraim Park <ephiep...@fb.com>
---
 kernel/events/core.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5789810..623d38f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -722,11 +722,48 @@ static inline void __update_cgrp_time(struct perf_cgroup 
*cgrp)
        info->timestamp = now;
 }
 
+static inline void
+update_ancestor_cgroup_time(struct perf_event *event,
+                           struct perf_cgroup *cgrp,
+                           struct perf_cgroup_info *cgrp_info)
+{
+       if (!is_cgroup_event(event))
+               return;
+
+       if (cgroup_is_descendant(cgrp->css.cgroup,
+                                event->cgrp->css.cgroup) &&
+           event->cgrp != cgrp) {
+               struct perf_cgroup_info *info;
+
+               info = this_cpu_ptr(event->cgrp->info);
+               info->time += cgrp_info->timestamp - info->timestamp;
+               info->timestamp = cgrp_info->timestamp;
+       }
+}
+
 static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context 
*cpuctx)
 {
        struct perf_cgroup *cgrp_out = cpuctx->cgrp;
-       if (cgrp_out)
+
+       if (cgrp_out) {
                __update_cgrp_time(cgrp_out);
+
+               /* update time for ancestor cgroups */
+               if (cgrp_out->css.cgroup->level > 1) {
+                       struct perf_cgroup_info *info
+                               = this_cpu_ptr(cgrp_out->info);
+                       struct perf_event *event;
+
+                       list_for_each_entry(event, &cpuctx->ctx.pinned_groups,
+                                           group_entry)
+                               update_ancestor_cgroup_time(event, cgrp_out,
+                                                           info);
+                       list_for_each_entry(event, &cpuctx->ctx.flexible_groups,
+                                           group_entry)
+                               update_ancestor_cgroup_time(event, cgrp_out,
+                                                           info);
+               }
+       }
 }
 
 static inline void update_cgrp_time_from_event(struct perf_event *event)
@@ -749,6 +786,24 @@ static inline void update_cgrp_time_from_event(struct 
perf_event *event)
 }
 
 static inline void
+perf_ancestor_cgroup_set_timestamp(struct perf_event *event,
+                                  struct perf_cgroup *cgrp,
+                                  struct perf_cgroup_info *cgrp_info)
+{
+       if (!is_cgroup_event(event))
+               return;
+
+       if (cgroup_is_descendant(cgrp->css.cgroup,
+                                event->cgrp->css.cgroup) &&
+           event->cgrp != cgrp) {
+               struct perf_cgroup_info *info
+                       = this_cpu_ptr(event->cgrp->info);
+
+               info->timestamp = cgrp_info->timestamp;
+       }
+}
+
+static inline void
 perf_cgroup_set_timestamp(struct task_struct *task,
                          struct perf_event_context *ctx)
 {
@@ -766,6 +821,17 @@ perf_cgroup_set_timestamp(struct task_struct *task,
        cgrp = perf_cgroup_from_task(task, ctx);
        info = this_cpu_ptr(cgrp->info);
        info->timestamp = ctx->timestamp;
+
+       /* set timestamp for ancestor cgroups */
+       if (cgrp->css.cgroup->level > 1) {
+               struct perf_cgroup_info *info = this_cpu_ptr(cgrp->info);
+               struct perf_event *event;
+
+               list_for_each_entry(event, &ctx->pinned_groups, group_entry)
+                       perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
+               list_for_each_entry(event, &ctx->flexible_groups, group_entry)
+                       perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
+       }
 }
 
 static DEFINE_PER_CPU(struct list_head, cgrp_cpuctx_list);
-- 
2.9.5