| Message ID | 20240406092005.92399-1-andrea.righi@canonical.com |
|---|---|
| Headers | show |
| Series | libbpf: API to partially consume items from ringbuffer | expand |
On Sat, Apr 06, 2024 at 10:52:10AM -0700, Andrii Nakryiko wrote: > On Sat, Apr 6, 2024 at 10:39 AM Andrii Nakryiko > <andrii.nakryiko@gmail.com> wrote: > > > > On Sat, Apr 6, 2024 at 2:20 AM Andrea Righi <andrea.righi@canonical.com> wrote: > > > > > > Add tests for new API ring__consume_n() and ring_buffer__consume_n(). > > > > > > Signed-off-by: Andrea Righi <andrea.righi@canonical.com> > > > --- > > > tools/testing/selftests/bpf/prog_tests/ringbuf.c | 8 ++++++++ > > > 1 file changed, 8 insertions(+) > > > > > > diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c > > > index 48c5695b7abf..33aba7684ab9 100644 > > > --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c > > > +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c > > > @@ -304,10 +304,18 @@ static void ringbuf_subtest(void) > > > err = ring_buffer__consume(ringbuf); > > > CHECK(err < 0, "rb_consume", "failed: %d\b", err); > > > > > > + /* try to consume up to one item */ > > > + err = ring_buffer__consume_n(ringbuf, 1); > > > + CHECK(err < 0 || err > 1, "rb_consume_n", "failed: %d\b", err); > > > + > > > /* also consume using ring__consume to make sure it works the same */ > > > err = ring__consume(ring); > > > ASSERT_GE(err, 0, "ring_consume"); > > > > > > + /* try to consume up to one item */ > > > + err = ring__consume_n(ring, 1); > > > + CHECK(err < 0 || err > 1, "ring_consume_n", "failed: %d\b", err); > > > + > > > > Did you actually run this test? There is ring_buffer__consume() and > > ring__consume() calls right before your added calls, so consume_n will > > return zero. > > > > I dropped this broken patch. Please send a proper test as a follow up. > > Sorry, technically, it's not broken, it just doesn't test much (CHECK > conditions confused me, I didn't realize you allow zero initially). We > will never consume anything and the result will be zero, which isn't > very meaningful. > > "Interesting" test would set up things so that we have >1 item in > ringbuf and we consume exactly one at a time, because that's the new > logic you added. > > I think it will be simpler to add a dedicated and simpler ringbuf test > for this, where you can specify how many items to submit, and then do > a bunch of consume/consume_n invocations, checking exact results. > > Plus, please don't add new CHECK() uses, use ASSERT_XXX() ones instead. > > I've applied first three patches because they look correct and it's > good to setup libbpf 1.5 dev cycle, but please do follow up with a > better test. Thanks. Yeah, sorry, I tried to add a minimal test to the existing one, but I agree that it not very meaningful. I already have a better dedicated test case for this (https://github.com/arighi/ebpf-maps/blob/libbpf-consume-n/src/main.c#L118), I just need to integrate it in the kselftest properly (and maybe pre-generate more than N records in the ring buffer, so that we can better test if the limit works as expected). I'll send another patch to add a proper test case. Thanks for applying the other patches! -Andrea > > > > > > /* 3 rounds, 2 samples each */ > > > cnt = atomic_xchg(&sample_cnt, 0); > > > CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt); > > > -- > > > 2.43.0 > > >
Introduce ring__consume_n() and ring_buffer__consume_n() API to partially consume items from one (or more) ringbuffer(s). This can be useful, for example, to consume just a single item or when we need to copy multiple items to a limited user-space buffer from the ringbuffer callback. Practical example (where this API can be used): https://github.com/sched-ext/scx/blob/b7c06b9ed9f72cad83c31e39e9c4e2cfd8683a55/rust/scx_rustland_core/src/bpf.rs#L217 See also: https://lore.kernel.org/lkml/20240310154726.734289-1-andrea.righi@canonical.com/T/#u v4: - add a selftest to test the new API - open a new 1.5.0 cycle v3: - rename ring__consume_max() -> ring__consume_n() and ring_buffer__consume_max() -> ring_buffer__consume_n() - add new API to a new 1.5.0 cycle - fixed minor nits / comments v2: - introduce a new API instead of changing the callback's retcode behavior Andrea Righi (4): libbpf: Start v1.5 development cycle libbpf: ringbuf: allow to consume up to a certain amount of items libbpf: Add ring__consume_n / ring_buffer__consume_n selftests/bpf: Add tests for ring__consume_n and ring_buffer__consume_n tools/lib/bpf/libbpf.h | 12 +++++ tools/lib/bpf/libbpf.map | 6 +++ tools/lib/bpf/libbpf_version.h | 2 +- tools/lib/bpf/ringbuf.c | 59 ++++++++++++++++++++---- tools/testing/selftests/bpf/prog_tests/ringbuf.c | 8 ++++ 5 files changed, 76 insertions(+), 11 deletions(-)