We already provide ring_buffer__epoll_fd to enable use of external
polling systems. However, the only API available to consume the ring
buffer is ring_buffer__consume, which always checks all rings. When
polling for many events, this can be wasteful.
Signed-off-by: Adam Sindelar <[email protected]>
---
v1->v2: Added entry to libbpf.map
v2->v3: Correctly set errno and handle overflow
v3->v4: Fixed an embarrasing typo from zealous autocomplete
tools/lib/bpf/libbpf.h | 1 +
tools/lib/bpf/libbpf.map | 1 +
tools/lib/bpf/ringbuf.c | 22 ++++++++++++++++++++++
3 files changed, 24 insertions(+)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 55b97b2087540..20ccc65eb3f9d 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1195,6 +1195,7 @@ 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_ring(struct ring_buffer *rb, uint32_t ring_id);
LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
struct user_ring_buffer_opts {
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 9c7538dd5835e..42dc418b4672f 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -398,4 +398,5 @@ LIBBPF_1.3.0 {
bpf_prog_detach_opts;
bpf_program__attach_netfilter;
bpf_program__attach_tcx;
+ ring_buffer__consume_ring;
} LIBBPF_1.2.0;
diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 02199364db136..457469fc7d71e 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -290,6 +290,28 @@ int ring_buffer__consume(struct ring_buffer *rb)
return res;
}
+/* Consume available data from a single RINGBUF map identified by its ID.
+ * The ring ID is returned in epoll_data by epoll_wait when called with
+ * ring_buffer__epoll_fd.
+ */
+int ring_buffer__consume_ring(struct ring_buffer *rb, uint32_t ring_id)
+{
+ struct ring *ring;
+ int64_t res;
+
+ if (ring_id >= rb->ring_cnt)
+ return libbpf_err(-EINVAL);
+
+ ring = &rb->rings[ring_id];
+ res = ringbuf_process_ring(ring);
+ if (res < 0)
+ return libbpf_err(res);
+
+ if (res > INT_MAX)
+ return INT_MAX;
+ return res;
+}
+
/* Poll for available data and consume records, if any are available.
* Returns number of records consumed (or INT_MAX, whichever is less), or
* negative number, if any of the registered callbacks returned error.
--
2.39.2
Adam Sindelar wrote:
> We already provide ring_buffer__epoll_fd to enable use of external
> polling systems. However, the only API available to consume the ring
> buffer is ring_buffer__consume, which always checks all rings. When
> polling for many events, this can be wasteful.
>
> Signed-off-by: Adam Sindelar <[email protected]>
> ---
> v1->v2: Added entry to libbpf.map
> v2->v3: Correctly set errno and handle overflow
> v3->v4: Fixed an embarrasing typo from zealous autocomplete
>
> tools/lib/bpf/libbpf.h | 1 +
> tools/lib/bpf/libbpf.map | 1 +
> tools/lib/bpf/ringbuf.c | 22 ++++++++++++++++++++++
> 3 files changed, 24 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 55b97b2087540..20ccc65eb3f9d 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -1195,6 +1195,7 @@ 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_ring(struct ring_buffer *rb, uint32_t ring_id);
> LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
>
> struct user_ring_buffer_opts {
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 9c7538dd5835e..42dc418b4672f 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -398,4 +398,5 @@ LIBBPF_1.3.0 {
> bpf_prog_detach_opts;
> bpf_program__attach_netfilter;
> bpf_program__attach_tcx;
> + ring_buffer__consume_ring;
> } LIBBPF_1.2.0;
> diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
> index 02199364db136..457469fc7d71e 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -290,6 +290,28 @@ int ring_buffer__consume(struct ring_buffer *rb)
> return res;
> }
>
> +/* Consume available data from a single RINGBUF map identified by its ID.
> + * The ring ID is returned in epoll_data by epoll_wait when called with
> + * ring_buffer__epoll_fd.
> + */
> +int ring_buffer__consume_ring(struct ring_buffer *rb, uint32_t ring_id)
> +{
> + struct ring *ring;
> + int64_t res;
> +
> + if (ring_id >= rb->ring_cnt)
> + return libbpf_err(-EINVAL);
> +
> + ring = &rb->rings[ring_id];
> + res = ringbuf_process_ring(ring);
> + if (res < 0)
> + return libbpf_err(res);
> +
> + if (res > INT_MAX)
> + return INT_MAX;
> + return res;
Why not just return int64_t here? Then skip the INT_MAX check? I would
just assume get the actual value if I was calling this.
> +}
> +
> /* Poll for available data and consume records, if any are available.
> * Returns number of records consumed (or INT_MAX, whichever is less), or
> * negative number, if any of the registered callbacks returned error.
> --
> 2.39.2
>
>
On Thu, Jul 27, 2023 at 12:00:10PM -0700, John Fastabend wrote:
> Adam Sindelar wrote:
> > We already provide ring_buffer__epoll_fd to enable use of external
> > polling systems. However, the only API available to consume the ring
> > buffer is ring_buffer__consume, which always checks all rings. When
> > polling for many events, this can be wasteful.
> >
> > Signed-off-by: Adam Sindelar <[email protected]>
> > ---
> > v1->v2: Added entry to libbpf.map
> > v2->v3: Correctly set errno and handle overflow
> > v3->v4: Fixed an embarrasing typo from zealous autocomplete
> >
> > tools/lib/bpf/libbpf.h | 1 +
> > tools/lib/bpf/libbpf.map | 1 +
> > tools/lib/bpf/ringbuf.c | 22 ++++++++++++++++++++++
> > 3 files changed, 24 insertions(+)
> >
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index 55b97b2087540..20ccc65eb3f9d 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -1195,6 +1195,7 @@ 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_ring(struct ring_buffer *rb, uint32_t ring_id);
> > LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
> >
> > struct user_ring_buffer_opts {
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 9c7538dd5835e..42dc418b4672f 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -398,4 +398,5 @@ LIBBPF_1.3.0 {
> > bpf_prog_detach_opts;
> > bpf_program__attach_netfilter;
> > bpf_program__attach_tcx;
> > + ring_buffer__consume_ring;
> > } LIBBPF_1.2.0;
> > diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
> > index 02199364db136..457469fc7d71e 100644
> > --- a/tools/lib/bpf/ringbuf.c
> > +++ b/tools/lib/bpf/ringbuf.c
> > @@ -290,6 +290,28 @@ int ring_buffer__consume(struct ring_buffer *rb)
> > return res;
> > }
> >
> > +/* Consume available data from a single RINGBUF map identified by its ID.
> > + * The ring ID is returned in epoll_data by epoll_wait when called with
> > + * ring_buffer__epoll_fd.
> > + */
> > +int ring_buffer__consume_ring(struct ring_buffer *rb, uint32_t ring_id)
> > +{
> > + struct ring *ring;
> > + int64_t res;
> > +
> > + if (ring_id >= rb->ring_cnt)
> > + return libbpf_err(-EINVAL);
> > +
> > + ring = &rb->rings[ring_id];
> > + res = ringbuf_process_ring(ring);
> > + if (res < 0)
> > + return libbpf_err(res);
> > +
> > + if (res > INT_MAX)
> > + return INT_MAX;
> > + return res;
>
> Why not just return int64_t here? Then skip the INT_MAX check? I would
> just assume get the actual value if I was calling this.
>
Mainly for consistency with the existing API. So far, the comparable
LIBBPF_API functions use int. It's hard to imagine that the number of
records would exceed ~2 billion in a single call - I think the
abberation is that ringbuf_process_ring using a 64-bit counter. If you
do exceed INT_MAX records, something is probably wrong and maybe the function
should return error instead. (But that would be outside the scope of
this patch.)
> > +}
> > +
> > /* Poll for available data and consume records, if any are available.
> > * Returns number of records consumed (or INT_MAX, whichever is less), or
> > * negative number, if any of the registered callbacks returned error.
> > --
> > 2.39.2
> >
> >
>
>
On 7/27/23 1:34 AM, Adam Sindelar wrote:
> We already provide ring_buffer__epoll_fd to enable use of external
> polling systems. However, the only API available to consume the ring
> buffer is ring_buffer__consume, which always checks all rings. When
> polling for many events, this can be wasteful.
>
> Signed-off-by: Adam Sindelar <[email protected]>
> ---
> v1->v2: Added entry to libbpf.map
> v2->v3: Correctly set errno and handle overflow
> v3->v4: Fixed an embarrasing typo from zealous autocomplete
>
> tools/lib/bpf/libbpf.h | 1 +
> tools/lib/bpf/libbpf.map | 1 +
> tools/lib/bpf/ringbuf.c | 22 ++++++++++++++++++++++
> 3 files changed, 24 insertions(+)
Could you add a selftest to exercise ring_buffer__consume_ring()?
This way, people can better understand how this API could be used.
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 55b97b2087540..20ccc65eb3f9d 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -1195,6 +1195,7 @@ 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_ring(struct ring_buffer *rb, uint32_t ring_id);
> LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
>
[...]
On Thu, Jul 27, 2023 at 03:11:00PM -0700, Yonghong Song wrote:
>
>
> On 7/27/23 1:34 AM, Adam Sindelar wrote:
> > We already provide ring_buffer__epoll_fd to enable use of external
> > polling systems. However, the only API available to consume the ring
> > buffer is ring_buffer__consume, which always checks all rings. When
> > polling for many events, this can be wasteful.
> >
> > Signed-off-by: Adam Sindelar <[email protected]>
> > ---
> > v1->v2: Added entry to libbpf.map
> > v2->v3: Correctly set errno and handle overflow
> > v3->v4: Fixed an embarrasing typo from zealous autocomplete
> >
> > tools/lib/bpf/libbpf.h | 1 +
> > tools/lib/bpf/libbpf.map | 1 +
> > tools/lib/bpf/ringbuf.c | 22 ++++++++++++++++++++++
> > 3 files changed, 24 insertions(+)
>
> Could you add a selftest to exercise ring_buffer__consume_ring()?
> This way, people can better understand how this API could be used.
>
Yes, will do - I'll try to send out v5 with a test case this afternoon.
As a note, I looked at the perf ring buffer API and it turns out Andrii
Nakryiko saw the same problem and solved in a similar way in 2020. (See
perf_buffer__consume_buffer).
> >
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index 55b97b2087540..20ccc65eb3f9d 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -1195,6 +1195,7 @@ 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_ring(struct ring_buffer *rb, uint32_t ring_id);
> > LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
> [...]