As the title suggests, this series adds bpf kfuncs for the cgroup CPU controller.
Motivation: Collecting cgroup statistics is expensive: the existing method is to open and parse a cgroup file. memcg already has an efficient alternative through BPF; this series extends that idea to cpu. Design: - Add bpf_css_flush_rstat() and bpf_cgroup_base_stat() to cgroup rstat. The second kfunc returns the raw cgroup_base_stat after the same cputime adjustment used by cpu.stat. - Leave reading the CFS bandwidth counters to the BPF program. They are plain fields of tg->cfs_bandwidth, so they need no kernel code. - Add bpf_css_to_task_group(), which returns a checked RCU pointer of the task_group*. This is usefule to compute the throttled time in bpf side since the bpf_per_cpu_ptr() requires a verifier-known struct task_group * and a pointer carrying the MEM_PERCPU property. This use the convention that task_group embeds its css at offset zero, so no scheduler helper or scheduler source change is needed. === Changes since v1: - Make the rstat flush generic, move it to rstat.c, and take a css. - Return cgroup_base_stat directly instead of repacking its CPU times. - Replace the throttled-time aggregation kfunc with a checked RCU cast in the CPU cgroup BPF code. The cast preserves the verifier type needed for the BPF program to perform the per-CPU sum itself. - Remove the changes in the scheduler part. Tested on VM with v7.2-rc5. Ziyang Men (2): cgroup: add BPF kfuncs to read a cpu cgroup's stats selftests/bpf: add cgroup_iter_cpu test for cpu cgroup kfuncs kernel/cgroup/Makefile | 2 + kernel/cgroup/bpf_cpu.c | 61 +++++ kernel/cgroup/rstat.c | 59 +++- tools/testing/selftests/bpf/cgroup_iter_cpu.h | 22 ++ tools/testing/selftests/bpf/config | 3 + .../bpf/prog_tests/cgroup_iter_cpu.c | 259 ++++++++++++++++++ .../selftests/bpf/progs/cgroup_iter_cpu.c | 113 ++++++++ 7 files changed, 517 insertions(+), 2 deletions(-) create mode 100644 kernel/cgroup/bpf_cpu.c create mode 100644 tools/testing/selftests/bpf/cgroup_iter_cpu.h create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_iter_cpu.c create mode 100644 tools/testing/selftests/bpf/progs/cgroup_iter_cpu.c -- 2.53.0-Meta
