[PATCH v2] perf stat: Support old kernels for bperf cgroup counting

Namhyung Kim
2022-10-11T05:28:08Z

The recent change in the cgroup will break the backward compatiblity in
the BPF program. It should support both old and new kernels using BPF
CO-RE technique.

Like the task_struct->__state handling in the offcpu analysis, we can
check the field name in the cgroup struct.

Acked-by: Jiri Olsa <jolsa-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Acked-by: Andrii Nakryiko <andrii-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Signed-off-by: Namhyung Kim <namhyung-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
tools/perf/util/bpf_skel/bperf_cgroup.bpf.c | 29 ++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
index 435a87556688..6a438e0102c5 100644
--- a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
+++ b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
@@ -43,6 +43,18 @@ struct {
__uint(value_size, sizeof(struct bpf_perf_event_value));
} cgrp_readings SEC(".maps");

+/* new kernel cgroup definition */
+struct cgroup___new {
+ int level;
+ struct cgroup *ancestors[];
+} __attribute__((preserve_access_index));
+
+/* old kernel cgroup definition */
+struct cgroup___old {
+ int level;
+ u64 ancestor_ids[];
+} __attribute__((preserve_access_index));
+
const volatile __u32 num_events = 1;
const volatile __u32 num_cpus = 1;

@@ -50,6 +62,21 @@ int enabled = 0;
int use_cgroup_v2 = 0;
int perf_subsys_id = -1;

+static inline __u64 get_cgroup_v1_ancestor_id(struct cgroup *cgrp, int level)
+{
+ /* recast pointer to capture new type for compiler */
+ struct cgroup___new *cgrp_new = (void *)cgrp;
+
+ if (bpf_core_field_exists(cgrp_new->ancestors)) {
+ return BPF_CORE_READ(cgrp_new, ancestors[level], kn, id);
+ } else {
+ /* recast pointer to capture old type for compiler */
+ struct cgroup___old *cgrp_old = (void *)cgrp;
+
+ return BPF_CORE_READ(cgrp_old, ancestor_ids[level]);
+ }
+}
+
static inline int get_cgroup_v1_idx(__u32 *cgrps, int size)
{
struct task_struct *p = (void *)bpf_get_current_task();
@@ -77,7 +104,7 @@ static inline int get_cgroup_v1_idx(__u32 *cgrps, int size)
break;

// convert cgroup-id to a map index
- cgrp_id = BPF_CORE_READ(cgrp, ancestors[i], kn, id);
+ cgrp_id = get_cgroup_v1_ancestor_id(cgrp, i);
elem = bpf_map_lookup_elem(&cgrp_idx, &cgrp_id);
if (!elem)
continue;
--
2.38.0.rc1.362.ged0d419d3c-goog