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Message-ID: <ip35p7p3hkskenndnbxt6gghzyfzmwdswo3mfaqisac7r57rlq@kqpp5ftzsdxi>
Date: Tue, 10 Sep 2024 14:59:48 -0600
From: Daniel Xu <dxu@...uu.xyz>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
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 Tue, Sep 10, 2024 at 11:36:36AM GMT, Alexei Starovoitov wrote:
> 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.
I'm actually unsure the difference, still. But all the other tests in
the file were using lskel so I just copy/pasted.
>
> Also pls split selftest into a separate patch.
Ack.
>
> >
> > # 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.
Ack.
>
> pw-bot: cr
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