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Subject[PATCH] perf: update perf_cgroup time for ancestor cgroup(s)
Date
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 <songliubraving@fb.com>
Reported-by: Ephraim Park <ephiepark@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
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