Commit a319185b authored by Yosry Ahmed's avatar Yosry Ahmed Committed by Alexei Starovoitov
Browse files

cgroup: bpf: enable bpf programs to integrate with rstat 



Enable bpf programs to make use of rstat to collect cgroup hierarchical
stats efficiently:
- Add cgroup_rstat_updated() kfunc, for bpf progs that collect stats.
- Add cgroup_rstat_flush() sleepable kfunc, for bpf progs that read stats.
- Add an empty bpf_rstat_flush() hook that is called during rstat
  flushing, for bpf progs that flush stats to attach to. Attaching a bpf
  prog to this hook effectively registers it as a flush callback.

Signed-off-by: default avatarYosry Ahmed <yosryahmed@google.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarHao Luo <haoluo@google.com>
Link: https://lore.kernel.org/r/20220824233117.1312810-4-haoluo@google.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent fe0dd9d4

kernel/cgroup/rstat.c

+48 −0
Original line number Diff line number Diff line
@@ -3,6 +3,10 @@ 


#include <linux/sched/cputime.h>



#include <linux/bpf.h>

#include <linux/btf.h>

#include <linux/btf_ids.h>



static DEFINE_SPINLOCK(cgroup_rstat_lock);

static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock);
@@ -141,6 +145,31 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos, 
	return pos;

}



/*

 * A hook for bpf stat collectors to attach to and flush their stats.

 * Together with providing bpf kfuncs for cgroup_rstat_updated() and

 * cgroup_rstat_flush(), this enables a complete workflow where bpf progs that

 * collect cgroup stats can integrate with rstat for efficient flushing.

 *

 * A static noinline declaration here could cause the compiler to optimize away

 * the function. A global noinline declaration will keep the definition, but may

 * optimize away the callsite. Therefore, __weak is needed to ensure that the

 * call is still emitted, by telling the compiler that we don't know what the

 * function might eventually be.

 *

 * __diag_* below are needed to dismiss the missing prototype warning.

 */

__diag_push();

__diag_ignore_all("-Wmissing-prototypes",

		  "kfuncs which will be used in BPF programs");



__weak noinline void bpf_rstat_flush(struct cgroup *cgrp,

				     struct cgroup *parent, int cpu)

{

}



__diag_pop();



/* see cgroup_rstat_flush() */

static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)

	__releases(&cgroup_rstat_lock) __acquires(&cgroup_rstat_lock)
@@ -168,6 +197,7 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep) 
			struct cgroup_subsys_state *css;



			cgroup_base_stat_flush(pos, cpu);

			bpf_rstat_flush(pos, cgroup_parent(pos), cpu);



			rcu_read_lock();

			list_for_each_entry_rcu(css, &pos->rstat_css_list,
@@ -501,3 +531,21 @@ void cgroup_base_stat_cputime_show(struct seq_file *seq) 
	seq_printf(seq, "core_sched.force_idle_usec %llu\n", forceidle_time);

#endif

}



/* Add bpf kfuncs for cgroup_rstat_updated() and cgroup_rstat_flush() */

BTF_SET8_START(bpf_rstat_kfunc_ids)

BTF_ID_FLAGS(func, cgroup_rstat_updated)

BTF_ID_FLAGS(func, cgroup_rstat_flush, KF_SLEEPABLE)

BTF_SET8_END(bpf_rstat_kfunc_ids)



static const struct btf_kfunc_id_set bpf_rstat_kfunc_set = {

	.owner          = THIS_MODULE,

	.set            = &bpf_rstat_kfunc_ids,

};



static int __init bpf_rstat_kfunc_init(void)

{

	return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,

					 &bpf_rstat_kfunc_set);

}

late_initcall(bpf_rstat_kfunc_init);