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

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Date:   Wed, 6 Oct 2021 17:35:28 -0700
From:   Song Liu <song@...nel.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Song Liu <songliubraving@...com>, 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 2:36 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> 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?

Aha, I copied this line from e31eec77e4ab90dcec7d2da93415f839098dc287. Will fix.

>
> > 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?

right... let me fix it in v2.

>
> > +                       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
> >