linux-kernel - Re: [PATCH v7 bpf-next RESEND 2/2] selftests/bpf: add bpf_read_branch

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Date:   Tue, 11 Feb 2020 11:30:01 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Xu <dxu@...uu.xyz>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        open list <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Peter Ziljstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v7 bpf-next RESEND 2/2] selftests/bpf: add
 bpf_read_branch_records() selftest

On Mon, Feb 10, 2020 at 12:09 PM Daniel Xu <dxu@...uu.xyz> wrote:
>
> Add a selftest to test:
>
> * default bpf_read_branch_records() behavior
> * BPF_F_GET_BRANCH_RECORDS_SIZE flag behavior
> * error path on non branch record perf events
> * using helper to write to stack
> * using helper to write to map
>
> On host with hardware counter support:
>
>     # ./test_progs -t perf_branches
>     #27/1 perf_branches_hw:OK
>     #27/2 perf_branches_no_hw:OK
>     #27 perf_branches:OK
>     Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED
>
> On host without hardware counter support (VM):
>
>     # ./test_progs -t perf_branches
>     #27/1 perf_branches_hw:OK
>     #27/2 perf_branches_no_hw:OK
>     #27 perf_branches:OK
>     Summary: 1/2 PASSED, 1 SKIPPED, 0 FAILED
>
> Also sync tools/include/uapi/linux/bpf.h.
>
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> ---
>  tools/include/uapi/linux/bpf.h                |  25 ++-
>  .../selftests/bpf/prog_tests/perf_branches.c  | 182 ++++++++++++++++++
>  .../selftests/bpf/progs/test_perf_branches.c  |  74 +++++++
>  3 files changed, 280 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/perf_branches.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_perf_branches.c
>

[...]

> +       /* generate some branches on cpu 0 */
> +       CPU_ZERO(&cpu_set);
> +       CPU_SET(0, &cpu_set);
> +       err = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
> +       if (CHECK(err, "set_affinity", "cpu #0, err %d\n", err))
> +               goto out_free_pb;
> +       /* spin the loop for a while (random high number) */
> +       for (i = 0; i < 1000000; ++i)
> +               ++j;
> +

test_perf_branches__detach here?

> +       /* read perf buffer */
> +       err = perf_buffer__poll(pb, 500);
> +       if (CHECK(err < 0, "perf_buffer__poll", "err %d\n", err))
> +               goto out_free_pb;
> +
> +       if (CHECK(!ok, "ok", "not ok\n"))
> +               goto out_free_pb;
> +

[...]

> diff --git a/tools/testing/selftests/bpf/progs/test_perf_branches.c b/tools/testing/selftests/bpf/progs/test_perf_branches.c
> new file mode 100644
> index 000000000000..60327d512400
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_perf_branches.c
> @@ -0,0 +1,74 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2019 Facebook
> +
> +#include <stddef.h>
> +#include <linux/ptrace.h>
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_trace_helpers.h"
> +
> +struct fake_perf_branch_entry {
> +       __u64 _a;
> +       __u64 _b;
> +       __u64 _c;
> +};
> +
> +struct output {
> +       int required_size;
> +       int written_stack;
> +       int written_map;
> +};
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
> +       __uint(key_size, sizeof(int));
> +       __uint(value_size, sizeof(int));
> +} perf_buf_map SEC(".maps");
> +
> +typedef struct fake_perf_branch_entry fpbe_t[30];
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_ARRAY);
> +       __uint(max_entries, 1);
> +       __type(key, __u32);
> +       __type(value, fpbe_t);
> +} scratch_map SEC(".maps");

Can you please use global variables instead of array and
perf_event_array? Would make BPF side clearer and userspace simpler.
struct output member will just become variables.

[...]