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From: "Daniel Xu" <dxu@dxuuu.xyz>
To: "Andrii Nakryiko" <andrii.nakryiko@gmail.com>
Cc: "bpf" <bpf@vger.kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"Andrii Nakryiko" <andriin@fb.com>,
	"open list" <linux-kernel@vger.kernel.org>,
	"Kernel Team" <kernel-team@fb.com>,
	"Peter Ziljstra" <peterz@infradead.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>
Subject: Re: [PATCH v7 bpf-next RESEND 2/2] selftests/bpf: add bpf_read_branch_records() selftest
Date: Thu, 13 Feb 2020 23:05:03 -0800
Message-ID: <C0LP269G4WO4.1Q4M8CK4K92SU@dlxu-fedora-R90QNFJV> (raw)
In-Reply-To: <CAEf4BzZfGXHL36ntjkQsTTEEa9yzqnS=Xs4XCibejpo5AKGpuQ@mail.gmail.com>

On Tue Feb 11, 2020 at 11:30 AM, Andrii Nakryiko wrote:
> On Mon, Feb 10, 2020 at 12:09 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
[...]

> 
> > +       /* 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?

Yeah, good idea.

[...]

> > +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

If you mean `scratch_map`, sure.

> and perf_event_array?

Do you mean replace the perf ring buffer with global variables? I think
that would limit the number of samples we validate in userspace to a fixed
number. It might be better to validate as many as the system gives us.

Let me know what you think. I might be overthinking it.

> Would make BPF side clearer and userspace simpler.
> struct output member will just become variables.


Thanks,
Daniel

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-10 20:07 [PATCH v7 bpf-next RESEND 0/2] Add bpf_read_branch_records() helper Daniel Xu
2020-02-10 20:07 ` [PATCH v7 bpf-next RESEND 1/2] bpf: " Daniel Xu
2020-02-11 19:23   ` Andrii Nakryiko
2020-02-14  6:34     ` Daniel Xu
2020-02-10 20:07 ` [PATCH v7 bpf-next RESEND 2/2] selftests/bpf: add bpf_read_branch_records() selftest Daniel Xu
2020-02-11 19:30   ` Andrii Nakryiko
2020-02-14  7:05     ` Daniel Xu [this message]
2020-02-14 17:47       ` Andrii Nakryiko

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