netdev - Re: [PATCH] selftests/bpf: skip get_branch

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Date:   Wed, 6 Oct 2021 14:35:25 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH] selftests/bpf: skip get_branch_snapshot in vm

On Wed, Oct 6, 2021 at 1:31 PM Song Liu <songliubraving@...com> wrote:
>
> VMs running on latest kernel support LBR. However, bpf_get_branch_snapshot
> couldn't stop the LBR before too many entries are flushed. Skip the test
> for VMs before we find a proper fix for VMs.
>
> Read the "flags" line from /proc/cpuinfo, if it contains "hypervisor",
> skip test get_branch_snapshot.
>
> Fixes: 025bd7c753aa (selftests/bpf: Add test for bpf_get_branch_snapshot)

missing quotes?

> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  .../bpf/prog_tests/get_branch_snapshot.c      | 32 +++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> index 67e86f8d86775..bf9d47a859449 100644
> --- a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> +++ b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> @@ -6,6 +6,30 @@
>  static int *pfd_array;
>  static int cpu_cnt;
>
> +static bool is_hypervisor(void)
> +{
> +       char *line = NULL;
> +       bool ret = false;
> +       size_t len;
> +       FILE *fp;
> +
> +       fp = fopen("/proc/cpuinfo", "r");
> +       if (!fp)
> +               return false;
> +
> +       while (getline(&line, &len, fp) != -1) {
> +               if (strstr(line, "flags") == line) {

strncmp() would be more explicit. That's what you are trying to do
(prefix match), right?

> +                       if (strstr(line, "hypervisor") != NULL)
> +                               ret = true;
> +                       break;
> +               }
> +       }
> +
> +       free(line);
> +       fclose(fp);
> +       return ret;
> +}
> +
>  static int create_perf_events(void)
>  {
>         struct perf_event_attr attr = {0};
> @@ -54,6 +78,14 @@ void test_get_branch_snapshot(void)
>         struct get_branch_snapshot *skel = NULL;
>         int err;
>
> +       if (is_hypervisor()) {
> +               /* As of today, LBR in hypervisor cannot be stopped before
> +                * too many entries are flushed. Skip the test for now in
> +                * hypervisor until we optimize the LBR in hypervisor.
> +                */
> +               test__skip();
> +               return;
> +       }
>         if (create_perf_events()) {
>                 test__skip();  /* system doesn't support LBR */
>                 goto cleanup;
> --
> 2.30.2
>