Message-ID: <CAEf4BzY4YcQhZoz_ef4msZsF4gbT0yqu=bDZxW=1qxk+qKF98A@mail.gmail.com>
Date:   Tue, 25 Jun 2019 22:11:53 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: test perf buffer API

On Tue, Jun 25, 2019 at 4:26 PM Andrii Nakryiko <andriin@...com> wrote:
>
> Add test verifying perf buffer API functionality.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>  .../selftests/bpf/prog_tests/perf_buffer.c    | 86 +++++++++++++++++++
>  .../selftests/bpf/progs/test_perf_buffer.c    | 31 +++++++
>  2 files changed, 117 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/perf_buffer.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_perf_buffer.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/perf_buffer.c b/tools/testing/selftests/bpf/prog_tests/perf_buffer.c
> new file mode 100644
> index 000000000000..3ba3e26141ac
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/perf_buffer.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +#include <pthread.h>
> +#include <sched.h>
> +#include <sys/socket.h>
> +#include <test_progs.h>
> +
> +static void on_sample(void *ctx, void *data, __u32 size)
> +{
> +       cpu_set_t *cpu_seen = ctx;
> +       int cpu = *(int *)data;
> +
> +       CPU_SET(cpu, cpu_seen);
> +}
> +
> +void test_perf_buffer(void)
> +{
> +       int err, prog_fd, prog_pfd, nr_cpus, i, duration = 0;
> +       const char *prog_name = "kprobe/sys_nanosleep";
> +       const char *file = "./test_perf_buffer.o";
> +       struct bpf_map *perf_buf_map;
> +       cpu_set_t cpu_set, cpu_seen;
> +       struct bpf_program *prog;
> +       struct bpf_object *obj;
> +       struct perf_buffer *pb;
> +
> +       nr_cpus = libbpf_num_possible_cpus();
> +       if (CHECK(nr_cpus < 0, "nr_cpus", "err %d\n", nr_cpus))
> +               return;
> +
> +       /* load program */
> +       err = bpf_prog_load(file, BPF_PROG_TYPE_KPROBE, &obj, &prog_fd);
> +       if (CHECK(err, "obj_load", "err %d errno %d\n", err, errno))
> +               return;
> +
> +       prog = bpf_object__find_program_by_title(obj, prog_name);
> +       if (CHECK(!prog, "find_probe", "prog '%s' not found\n", prog_name))
> +               goto out_close;
> +
> +       /* load map */
> +       perf_buf_map = bpf_object__find_map_by_name(obj, "perf_buf_map");
> +       if (CHECK(!perf_buf_map, "find_perf_buf_map", "not found\n"))
> +               goto out_close;
> +
> +       /* attach kprobe */
> +       prog_pfd = bpf_program__attach_kprobe(prog, false /* retprobe */,
> +                                             "sys_nanosleep");
> +       if (CHECK(prog_pfd < 0, "attach_kprobe", "err %d\n", prog_pfd))
> +               goto out_close;
> +
> +       /* set up perf buffer */
> +       pb = perf_buffer__new(perf_buf_map, 1, on_sample, NULL, &cpu_seen);
> +       if (CHECK(IS_ERR(pb), "perf_buf__new", "err %ld\n", PTR_ERR(pb)))
> +               goto out_detach;
> +
> +       /* trigger kprobe on every CPU */
> +       CPU_ZERO(&cpu_seen);
> +       for (i = 0; i < nr_cpus; i++) {
> +               CPU_ZERO(&cpu_set);
> +               CPU_SET(i, &cpu_set);
> +
> +               err = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set),
> +                                            &cpu_set);
> +               if (err && CHECK(err, "set_affinity", "cpu #%d, err %d\n",
> +                                i, err))
> +                       goto out_detach;
> +
> +               usleep(1);
> +       }
> +
> +       /* read perf buffer */
> +       err = perf_buffer__poll(pb, 100);
> +       if (CHECK(err < 0, "perf_buffer__poll", "err %d\n", err))
> +               goto out_free_pb;
> +
> +       if (CHECK(CPU_COUNT(&cpu_seen) != nr_cpus, "seen_cpu_cnt",
> +                 "expect %d, seen %d\n", nr_cpus, CPU_COUNT(&cpu_seen)))
> +               goto out_free_pb;
> +
> +out_free_pb:
> +       perf_buffer__free(pb);
> +out_detach:
> +       libbpf_perf_event_disable_and_close(prog_pfd);
> +out_close:
> +       bpf_object__close(obj);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_perf_buffer.c b/tools/testing/selftests/bpf/progs/test_perf_buffer.c
> new file mode 100644
> index 000000000000..ba961f608fd5
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_perf_buffer.c
> @@ -0,0 +1,31 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2019 Facebook
> +
> +#include <linux/ptrace.h>
> +#include <linux/bpf.h>
> +#include "bpf_helpers.h"
> +
> +struct {
> +       int type;
> +       int key_size;
> +       int value_size;
> +       int max_entries;
> +} perf_buf_map SEC(".maps") = {
> +       .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> +       .key_size = sizeof(int),
> +       .value_size = sizeof(int),
> +       .max_entries = 56,

Oh, this is not right, "works for me" only :). I've been meaning to
actually have another change to handle not specified max_entries (or
equivalently, max_entries == 0) to mean "all possible CPUs" for
BPF_MAP_TYPE_PERF_EVENT_ARRAY. Will produce v2 with that change.

> +};
> +
> +SEC("kprobe/sys_nanosleep")
> +int handle_sys_nanosleep_entry(struct pt_regs *ctx)
> +{
> +       int cpu = bpf_get_smp_processor_id();
> +
> +       bpf_perf_event_output(ctx, &perf_buf_map, BPF_F_CURRENT_CPU,
> +                             &cpu, sizeof(cpu));
> +       return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> +__u32 _version SEC("version") = 1;
> --
> 2.17.1
>

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