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/[email protected]/T/#u
[ Note: I haven't implemented the special case of n == 0 as "no limit",
because we still need to add a bunch of extra checks for INT_MAX, making
the code less readable and, from a performance perspective, it seems
that we may get more downsides than benefits, but I can try to look more
at this if you think it's worth it ]
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 (2):
libbpf: ringbuf: allow to consume up to a certain amount of items
libbpf: Add ring__consume_n / ring_buffer__consume_n
tools/lib/bpf/libbpf.h | 12 ++++++++++
tools/lib/bpf/libbpf.map | 6 +++++
tools/lib/bpf/ringbuf.c | 59 ++++++++++++++++++++++++++++++++++++++++--------
3 files changed, 67 insertions(+), 10 deletions(-)
Introduce a new API to consume items from a ring buffer, limited to a
specified amount, and return to the caller the actual number of items
consumed.
Link: https://lore.kernel.org/lkml/[email protected]/T
Signed-off-by: Andrea Righi <[email protected]>
---
tools/lib/bpf/libbpf.h | 12 ++++++++++++
tools/lib/bpf/libbpf.map | 6 ++++++
tools/lib/bpf/ringbuf.c | 38 +++++++++++++++++++++++++++++++++++---
3 files changed, 53 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index f88ab50c0229..4f775a6dcaa0 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1293,6 +1293,7 @@ LIBBPF_API int ring_buffer__add(struct ring_buffer *rb, int map_fd,
ring_buffer_sample_fn sample_cb, void *ctx);
LIBBPF_API int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms);
LIBBPF_API int ring_buffer__consume(struct ring_buffer *rb);
+LIBBPF_API int ring_buffer__consume_n(struct ring_buffer *rb, size_t n);
LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
/**
@@ -1367,6 +1368,17 @@ LIBBPF_API int ring__map_fd(const struct ring *r);
*/
LIBBPF_API int ring__consume(struct ring *r);
+/**
+ * @brief **ring__consume_n()** consumes up to a requested amount of items from
+ * a ringbuffer without event polling.
+ *
+ * @param r A ringbuffer object.
+ * @param n Maximum amount of items to consume.
+ * @return The number of items consumed, or a negative number if any of the
+ * callbacks return an error.
+ */
+LIBBPF_API int ring__consume_n(struct ring *r, size_t n);
+
struct user_ring_buffer_opts {
size_t sz; /* size of this struct, for forward/backward compatibility */
};
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 51732ecb1385..23d82bba021a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -416,3 +416,9 @@ LIBBPF_1.4.0 {
btf__new_split;
btf_ext__raw_data;
} LIBBPF_1.3.0;
+
+LIBBPF_1.5.0 {
+ global:
+ ring__consume_n;
+ ring_buffer__consume_n;
+} LIBBPF_1.4.0;
diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 2c4031168413..19cd34883011 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -277,6 +277,33 @@ static int64_t ringbuf_process_ring(struct ring *r, size_t n)
return cnt;
}
+/* Consume available ring buffer(s) data without event polling, up to n
+ * records.
+ *
+ * Returns number of records consumed across all registered ring buffers (or
+ * n, whichever is less), or negative number if any of the callbacks return
+ * error.
+ */
+int ring_buffer__consume_n(struct ring_buffer *rb, size_t n)
+{
+ int64_t err, res = 0;
+ int i;
+
+ for (i = 0; i < rb->ring_cnt; i++) {
+ struct ring *ring = rb->rings[i];
+
+ err = ringbuf_process_ring(ring, n);
+ if (err < 0)
+ return libbpf_err(err);
+ res += err;
+ n -= err;
+
+ if (n == 0)
+ break;
+ }
+ return res;
+}
+
/* Consume available ring buffer(s) data without event polling.
* Returns number of records consumed across all registered ring buffers (or
* INT_MAX, whichever is less), or negative number if any of the callbacks
@@ -378,17 +405,22 @@ int ring__map_fd(const struct ring *r)
return r->map_fd;
}
-int ring__consume(struct ring *r)
+int ring__consume_n(struct ring *r, size_t n)
{
- int64_t res;
+ int res;
- res = ringbuf_process_ring(r, INT_MAX);
+ res = ringbuf_process_ring(r, n);
if (res < 0)
return libbpf_err(res);
return res > INT_MAX ? INT_MAX : res;
}
+int ring__consume(struct ring *r)
+{
+ return ring__consume_n(r, INT_MAX);
+}
+
static void user_ringbuf_unmap_ring(struct user_ring_buffer *rb)
{
if (rb->consumer_pos) {
--
2.43.0
On Fri, Apr 5, 2024 at 3:36 PM Andrea Righi <andrea.righi@canonicalcom> wrote:
>
> 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/[email protected]/T/#u
>
> [ Note: I haven't implemented the special case of n == 0 as "no limit",
> because we still need to add a bunch of extra checks for INT_MAX, making
> the code less readable and, from a performance perspective, it seems
> that we may get more downsides than benefits, but I can try to look more
> at this if you think it's worth it ]
>
> 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
You also need to update Makefile, CI is failing right now ([0]).
Please also add a simple test to BPF selftests using the new API.
Other than that the changes look good.
[0] https://github.com/kernel-patches/bpf/actions/runs/8576515495/job/23507610313#step:11:73
pw-bot: cr
> - fixed minor nits / comments
>
> v2:
> - introduce a new API instead of changing the callback's retcode
> behavior
>
> Andrea Righi (2):
> libbpf: ringbuf: allow to consume up to a certain amount of items
> libbpf: Add ring__consume_n / ring_buffer__consume_n
>
> tools/lib/bpf/libbpf.h | 12 ++++++++++
> tools/lib/bpf/libbpf.map | 6 +++++
> tools/lib/bpf/ringbuf.c | 59 ++++++++++++++++++++++++++++++++++++++++--------
> 3 files changed, 67 insertions(+), 10 deletions(-)
On Fri, Apr 05, 2024 at 04:16:34PM -0700, Andrii Nakryiko wrote:
> On Fri, Apr 5, 2024 at 3:36 PM Andrea Righi <[email protected]> wrote:
> >
> > 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/[email protected]/T/#u
> >
> > [ Note: I haven't implemented the special case of n == 0 as "no limit",
> > because we still need to add a bunch of extra checks for INT_MAX, making
> > the code less readable and, from a performance perspective, it seems
> > that we may get more downsides than benefits, but I can try to look more
> > at this if you think it's worth it ]
> >
> > 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
>
> You also need to update Makefile, CI is failing right now ([0]).
Yep, I wasn't sure if should have bumped up the version as well
(in libbpf_version.h). I'll add that.
>
> Please also add a simple test to BPF selftests using the new API.
> Other than that the changes look good.
Ok, will add a selftest.
Thanks,
-Andrea
>
> [0] https://github.com/kernel-patches/bpf/actions/runs/8576515495/job/23507610313#step:11:73
>
> pw-bot: cr
>
> > - fixed minor nits / comments
> >
> > v2:
> > - introduce a new API instead of changing the callback's retcode
> > behavior
> >
> > Andrea Righi (2):
> > libbpf: ringbuf: allow to consume up to a certain amount of items
> > libbpf: Add ring__consume_n / ring_buffer__consume_n
> >
> > tools/lib/bpf/libbpf.h | 12 ++++++++++
> > tools/lib/bpf/libbpf.map | 6 +++++
> > tools/lib/bpf/ringbuf.c | 59 ++++++++++++++++++++++++++++++++++++++++--------
> > 3 files changed, 67 insertions(+), 10 deletions(-)