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.
Expose the CPU controller's per-cgroup statistics to BPF, following the memory controller kfuncs in mm/bpf_memcontrol.c. 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. Suggested-by: Shakeel Butt <[email protected]> Suggested-by: Tejun Heo <[email protected]> Assisted-by: Claude:claude-opus-5 Signed-off-by: Ziyang Men <[email protected]> --- kernel/cgroup/Makefile | 2 ++ kernel/cgroup/bpf_cpu.c | 61 +++++++++++++++++++++++++++++++++++++++++ kernel/cgroup/rstat.c | 59 +++++++++++++++++++++++++++++++++++++-- 3 files changed, 120 insertions(+), 2 deletions(-) create mode 100644 kernel/cgroup/bpf_cpu.c diff --git a/kernel/cgroup/Makefile b/kernel/cgroup/Makefile index ede31601a363..0ba59b7eef48 100644 --- a/kernel/cgroup/Makefile +++ b/kernel/cgroup/Makefile @@ -1,6 +1,8 @@ # SPDX-License-Identifier: GPL-2.0 obj-y := cgroup.o rstat.o namespace.o cgroup-v1.o freezer.o +obj-$(CONFIG_BPF_SYSCALL) += bpf_cpu.o + obj-$(CONFIG_CGROUP_FREEZER) += legacy_freezer.o obj-$(CONFIG_CGROUP_PIDS) += pids.o obj-$(CONFIG_CGROUP_RDMA) += rdma.o diff --git a/kernel/cgroup/bpf_cpu.c b/kernel/cgroup/bpf_cpu.c new file mode 100644 index 000000000000..ac165d0b79ef --- /dev/null +++ b/kernel/cgroup/bpf_cpu.c @@ -0,0 +1,61 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * CPU controller BPF kfuncs + * + * Author: Ziyang Men <[email protected]> + */ + +#include <linux/bpf.h> +#include <linux/btf_ids.h> +#include <linux/cgroup.h> + +#ifdef CONFIG_CGROUP_SCHED +struct task_group; + +__bpf_kfunc_start_defs(); + +/** + * bpf_css_to_task_group - Cast a CPU controller css to its task group + * @css: CPU controller css + * + * Must be called under RCU. + * A C cast does not give the verifier a task_group pointer. This kfunc + * preserves the task_group and per-CPU types needed to read cfs_rq. + * + * Return: The task group, or NULL if @css belongs to another controller. + */ +__bpf_kfunc struct task_group * +bpf_css_to_task_group(struct cgroup_subsys_state *css) +{ + if (css->ss != &cpu_cgrp_subsys) + return NULL; + + /* task_group embeds css at offset zero. */ + return (struct task_group *)css; +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(bpf_cpu_cgroup_kfunc_ids) +BTF_ID_FLAGS(func, bpf_css_to_task_group, + KF_RCU | KF_RCU_PROTECTED | KF_RET_NULL) +BTF_KFUNCS_END(bpf_cpu_cgroup_kfunc_ids) + +static const struct btf_kfunc_id_set bpf_cpu_cgroup_kfunc_set = { + .owner = THIS_MODULE, + .set = &bpf_cpu_cgroup_kfunc_ids, +}; + +static int __init bpf_cpu_cgroup_kfunc_init(void) +{ + int err; + + err = register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, + &bpf_cpu_cgroup_kfunc_set); + if (err) + pr_warn("error while registering cpu cgroup kfuncs: %d\n", err); + + return err; +} +late_initcall(bpf_cpu_cgroup_kfunc_init); +#endif /* CONFIG_CGROUP_SCHED */ diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index de816a43db9f..46c322c4858b 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -752,6 +752,54 @@ void cgroup_base_stat_cputime_show(struct seq_file *seq) cgroup_force_idle_show(seq, &bstat); } +#ifdef CONFIG_BPF_SYSCALL + +__bpf_kfunc_start_defs(); + +/** + * bpf_css_flush_rstat - Flush a cgroup subsystem's rstat data + * @css: cgroup subsystem state to flush + */ +__bpf_kfunc void bpf_css_flush_rstat(struct cgroup_subsys_state *css) +{ + css_rstat_flush(css); +} + +/** + * bpf_cgroup_base_stat - Read a cgroup's base statistics + * @cgrp: cgroup to read from + * @out: zero-initialized output in nanoseconds + * + * CPU time is adjusted as for cpu.stat. + */ +__bpf_kfunc void bpf_cgroup_base_stat(struct cgroup *cgrp, + struct cgroup_base_stat *out) +{ + if (cgroup_parent(cgrp)) { + __css_rstat_lock(&cgrp->self, -1); + *out = cgrp->bstat; + cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime, + &out->cputime.utime, &out->cputime.stime); + __css_rstat_unlock(&cgrp->self, -1); + } else { + root_cgroup_cputime(out); + } +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(bpf_rstat_common_kfunc_ids) +BTF_ID_FLAGS(func, bpf_css_flush_rstat, KF_SLEEPABLE) +BTF_ID_FLAGS(func, bpf_cgroup_base_stat, KF_SLEEPABLE) +BTF_KFUNCS_END(bpf_rstat_common_kfunc_ids) + +static const struct btf_kfunc_id_set bpf_rstat_common_kfunc_set = { + .owner = THIS_MODULE, + .set = &bpf_rstat_common_kfunc_ids, +}; + +#endif /* CONFIG_BPF_SYSCALL */ + /* Add bpf kfuncs for css_rstat_updated() and css_rstat_flush() */ BTF_KFUNCS_START(bpf_rstat_kfunc_ids) BTF_ID_FLAGS(func, css_rstat_updated) @@ -765,7 +813,14 @@ static const struct btf_kfunc_id_set bpf_rstat_kfunc_set = { static int __init bpf_rstat_kfunc_init(void) { - return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, - &bpf_rstat_kfunc_set); + int ret; + + ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, + &bpf_rstat_kfunc_set); +#ifdef CONFIG_BPF_SYSCALL + ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, + &bpf_rstat_common_kfunc_set); +#endif + return ret; } late_initcall(bpf_rstat_kfunc_init); -- 2.53.0-Meta
