Re: [PATCH v5 bpf-next 2/4] bpf, docs: Add document for cpumask iter

[Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>]

On Wed, Jan 31, 2024 at 6:55 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> This patch adds the document for the newly added cpumask iterator
> kfuncs.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>


>  Documentation/bpf/cpumasks.rst | 60 ++++++++++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
>
> diff --git a/Documentation/bpf/cpumasks.rst b/Documentation/bpf/cpumasks.rst
> index b5d47a04da5d..5cedd719874c 100644
> --- a/Documentation/bpf/cpumasks.rst
> +++ b/Documentation/bpf/cpumasks.rst
> @@ -372,6 +372,66 @@ used.
>  .. _tools/testing/selftests/bpf/progs/cpumask_success.c:
>     https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/cpumask_success.c
>
> +3.3 cpumask iterator
> +--------------------
> +
> +The cpumask iterator facilitates the iteration of per-CPU data, including
> +runqueues, system_group_pcpu, and other such structures. To leverage the cpumask
> +iterator, one can employ the bpf_for_each() macro.
> +
> +Here's an example illustrating how to determine the number of running tasks on
> +each CPU.
> +
> +.. code-block:: c
> +
> +        /**
> +         * Here's an example demonstrating the functionality of the cpumask iterator.
> +         * We retrieve the cpumask associated with the specified pid, iterate through
> +         * its elements, and ultimately expose per-CPU data to userspace through a
> +         * seq file.
> +         */
> +        const struct rq runqueues __ksym __weak;
> +        u32 target_pid;
> +
> +        SEC("iter/cgroup")
> +        int BPF_PROG(cpu_cgroup, struct bpf_iter_meta *meta, struct cgroup *cgrp)
> +        {
> +                u32 nr_running = 0, nr_cpus = 0, nr_null_rq = 0;
> +                struct task_struct *p;
> +                struct rq *rq;
> +                int *cpu;
> +
> +                /* epilogue */
> +                if (cgrp == NULL)
> +                        return 0;
> +
> +                p = bpf_task_from_pid(target_pid);
> +                if (!p)
> +                        return 1;
> +
> +                BPF_SEQ_PRINTF(meta->seq, "%4s %s\n", "CPU", "nr_running");
> +                bpf_for_each(cpumask, cpu, p->cpus_ptr) {
> +                        rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, *cpu);
> +                        if (!rq) {
> +                                nr_null_rq += 1;
> +                                continue;
> +                        }
> +                        nr_cpus += 1;
> +
> +                        if (!rq->nr_running)
> +                                continue;
> +
> +                        nr_running += rq->nr_running;
> +                        BPF_SEQ_PRINTF(meta->seq, "%4u %u\n", *cpu, rq->nr_running);
> +                }
> +                BPF_SEQ_PRINTF(meta->seq, "Summary: nr_cpus %u, nr_running %u, nr_null_rq %u\n",
> +                               nr_cpus, nr_running, nr_null_rq);
> +
> +                bpf_task_release(p);
> +                return 0;
> +        }
> +
> +----
>
>  4. Adding BPF cpumask kfuncs
>  ============================
> --
> 2.39.1
>