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Message-ID: <CAADnVQKyfZ2-qCvmqG8z919ggdOszEjTs04H=cTGOZTi-zhx7Q@mail.gmail.com>
Date: Tue, 10 Sep 2024 11:36:36 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Daniel Xu <dxu@...uu.xyz>
Cc: Eddy Z <eddyz87@...il.com>, Andrii Nakryiko <andrii@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, Shuah Khan <shuah@...nel.org>,
John Fastabend <john.fastabend@...il.com>, Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Mykola Lysenko <mykolal@...com>, LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, Kernel Team <kernel-team@...a.com>
Subject: Re: [PATCH bpf-next] bpf: ringbuf: Support consuming
BPF_MAP_TYPE_RINGBUF from prog
On Mon, Sep 9, 2024 at 5:55 PM Daniel Xu <dxu@...uu.xyz> wrote:
>
> Right now there exists prog produce / userspace consume and userspace
> produce / prog consume support. But it is also useful to have prog
> produce / prog consume.
>
> For example, we want to track the latency overhead of cpumap in
> production. Since we need to store enqueue timestamps somewhere and
> cpumap is MPSC, we need an MPSC data structure to shadow cpumap. BPF
> ringbuf is such a data structure. Rather than reimplement (possibly
> poorly) a custom ringbuffer in BPF, extend the existing interface to
> allow the final quadrant of ringbuf usecases to be filled. Note we
> ignore userspace to userspace use case - there is no need to involve
> kernel for that.
>
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> ---
> kernel/bpf/verifier.c | 6 +-
> tools/testing/selftests/bpf/Makefile | 3 +-
> .../selftests/bpf/prog_tests/ringbuf.c | 50 +++++++++++++++
> .../bpf/progs/test_ringbuf_bpf_to_bpf.c | 64 +++++++++++++++++++
> 4 files changed, 120 insertions(+), 3 deletions(-)
> create mode 100644 tools/testing/selftests/bpf/progs/test_ringbuf_bpf_to_bpf.c
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 53d0556fbbf3..56bfe559f228 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -9142,7 +9142,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
> func_id != BPF_FUNC_ringbuf_query &&
> func_id != BPF_FUNC_ringbuf_reserve_dynptr &&
> func_id != BPF_FUNC_ringbuf_submit_dynptr &&
> - func_id != BPF_FUNC_ringbuf_discard_dynptr)
> + func_id != BPF_FUNC_ringbuf_discard_dynptr &&
> + func_id != BPF_FUNC_user_ringbuf_drain)
> goto error;
> break;
> case BPF_MAP_TYPE_USER_RINGBUF:
> @@ -9276,7 +9277,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
> goto error;
> break;
> case BPF_FUNC_user_ringbuf_drain:
> - if (map->map_type != BPF_MAP_TYPE_USER_RINGBUF)
> + if (map->map_type != BPF_MAP_TYPE_USER_RINGBUF &&
> + map->map_type != BPF_MAP_TYPE_RINGBUF)
> goto error;
I think it should work.
Andrii,
do you see any issues with such use?
> break;
> case BPF_FUNC_get_stackid:
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 9905e3739dd0..233109843d4d 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -503,7 +503,8 @@ LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h \
> LSKELS := fentry_test.c fexit_test.c fexit_sleep.c atomics.c \
> trace_printk.c trace_vprintk.c map_ptr_kern.c \
> core_kern.c core_kern_overflow.c test_ringbuf.c \
> - test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c
> + test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c \
> + test_ringbuf_bpf_to_bpf.c
Do you need it to be lskel ?
Regular skels are either to debug.
Also pls split selftest into a separate patch.
>
> # Generate both light skeleton and libbpf skeleton for these
> LSKELS_EXTRA := test_ksyms_module.c test_ksyms_weak.c kfunc_call_test.c \
> diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> index da430df45aa4..3e7955573ac5 100644
> --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> @@ -17,6 +17,7 @@
> #include "test_ringbuf_n.lskel.h"
> #include "test_ringbuf_map_key.lskel.h"
> #include "test_ringbuf_write.lskel.h"
> +#include "test_ringbuf_bpf_to_bpf.lskel.h"
>
> #define EDONE 7777
>
> @@ -497,6 +498,53 @@ static void ringbuf_map_key_subtest(void)
> test_ringbuf_map_key_lskel__destroy(skel_map_key);
> }
>
> +static void ringbuf_bpf_to_bpf_subtest(void)
> +{
> + struct test_ringbuf_bpf_to_bpf_lskel *skel;
> + int err, i;
> +
> + skel = test_ringbuf_bpf_to_bpf_lskel__open();
> + if (!ASSERT_OK_PTR(skel, "test_ringbuf_bpf_to_bpf_lskel__open"))
> + return;
> +
> + skel->maps.ringbuf.max_entries = getpagesize();
> + skel->bss->pid = getpid();
> +
> + err = test_ringbuf_bpf_to_bpf_lskel__load(skel);
> + if (!ASSERT_OK(err, "test_ringbuf_bpf_to_bpf_lskel__load"))
> + goto cleanup;
> +
> + ringbuf = ring_buffer__new(skel->maps.ringbuf.map_fd, NULL, NULL, NULL);
> + if (!ASSERT_OK_PTR(ringbuf, "ring_buffer__new"))
> + goto cleanup;
> +
> + err = test_ringbuf_bpf_to_bpf_lskel__attach(skel);
> + if (!ASSERT_OK(err, "test_ringbuf_bpf_to_bpf_lskel__attach"))
> + goto cleanup_ringbuf;
> +
> + /* Produce N_SAMPLES samples in the ring buffer by calling getpid() */
> + skel->bss->value = SAMPLE_VALUE;
> + for (i = 0; i < N_SAMPLES; i++)
> + syscall(__NR_getpgid);
> +
> + /* Trigger bpf-side consumption */
> + syscall(__NR_prctl);
This might conflict with other selftests that run in parallel.
Just load the skel and bpf_prog_run(prog_fd).
No need to attach anywhere in the kernel.
pw-bot: cr
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