linux-kernel - Re: [PATCH v5 bpf-next 2/2] selftests/bpf: add bpf_read_branch

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Message-Id: <C05FGIY6DS21.3FOPNFKMT6EWK@dlxu-fedora-R90QNFJV>
Date:   Sat, 25 Jan 2020 20:10:57 -0800
From:   "Daniel Xu" <dxu@...uu.xyz>
To:     "Alexei Starovoitov" <alexei.starovoitov@...il.com>
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>,
        "LKML" <linux-kernel@...r.kernel.org>,
        "Kernel Team" <kernel-team@...com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Arnaldo Carvalho de Melo" <acme@...nel.org>
Subject: Re: [PATCH v5 bpf-next 2/2] selftests/bpf: add
 bpf_read_branch_records() selftest

On Sat Jan 25, 2020 at 6:53 PM, Alexei Starovoitov wrote:
> On Sat, Jan 25, 2020 at 2:32 PM Daniel Xu <dxu@...uu.xyz> wrote:
> > +       attr.type = PERF_TYPE_HARDWARE;
> > +       attr.config = PERF_COUNT_HW_CPU_CYCLES;
> > +       attr.freq = 1;
> > +       attr.sample_freq = 4000;
> > +       attr.sample_type = PERF_SAMPLE_BRANCH_STACK;
> > +       attr.branch_sample_type = PERF_SAMPLE_BRANCH_USER | PERF_SAMPLE_BRANCH_ANY;
> > +       pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
> > +       if (CHECK(pfd < 0, "perf_event_open", "err %d\n", pfd))
> > +               goto out_destroy;
>
> 
> It's failing for me in kvm. Is there way to make it work?
> CIs will be vm based too. If this test requires physical host
> such test will keep failing in all such environments.
> Folks will be annoyed and eventually will disable the test.
> Can we figure out how to test in the vm from the start?

It seems there's a patchset that's adding LBR support to guest hosts:
https://lkml.org/lkml/2019/8/6/215 . However it seems to be stuck in
review limbo. Is there anything we can do to help that set along?

As far as hacking it, nothing really comes to mind. Seems that patchset
is our best hope.