2023-07-25 18:34:44

by Adam Sindelar

Subject: [PATCH] libbpf: Expose API to consume one ring at a time

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]>
---
tools/lib/bpf/libbpf.h | 1 +
tools/lib/bpf/ringbuf.c | 15 +++++++++++++++
2 files changed, 16 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/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 02199364db136..8d087bfc7d005 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -290,6 +290,21 @@ 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;
+
+ if (ring_id >= rb->ring_cnt)
+ return libbpf_err(-EINVAL);
+
+ ring = &rb->rings[ring_id];
+ return ringbuf_process_ring(ring);
+}
+
/* 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

2023-07-27 01:20:41

by Hou Tao

Subject: Re: [PATCH] libbpf: Expose API to consume one ring at a time

Hi,

On 7/26/2023 12:26 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]>
> ---
> tools/lib/bpf/libbpf.h | 1 +
> tools/lib/bpf/ringbuf.c | 15 +++++++++++++++
> 2 files changed, 16 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/ringbuf.c b/tools/lib/bpf/ringbuf.c
> index 02199364db136..8d087bfc7d005 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -290,6 +290,21 @@ 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;
> +
> + if (ring_id >= rb->ring_cnt)
> + return libbpf_err(-EINVAL);
> +
> + ring = &rb->rings[ring_id];
> + return ringbuf_process_ring(ring);

When ringbuf_process_ring() returns an error, we need to use
libbpf_err() to set the errno accordingly.
> +}
> +
> /* 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.

2023-07-27 06:41:20

by Hou Tao

Subject: Re: [PATCH] libbpf: Expose API to consume one ring at a time

Hi,

On 7/27/2023 9:06 AM, Hou Tao wrote:
> Hi,
>
> On 7/26/2023 12:26 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]>
>> ---
>> tools/lib/bpf/libbpf.h | 1 +
>> tools/lib/bpf/ringbuf.c | 15 +++++++++++++++
>> 2 files changed, 16 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/ringbuf.c b/tools/lib/bpf/ringbuf.c
>> index 02199364db136..8d087bfc7d005 100644
>> --- a/tools/lib/bpf/ringbuf.c
>> +++ b/tools/lib/bpf/ringbuf.c
>> @@ -290,6 +290,21 @@ 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;
>> +
>> + if (ring_id >= rb->ring_cnt)
>> + return libbpf_err(-EINVAL);
>> +
>> + ring = &rb->rings[ring_id];
>> + return ringbuf_process_ring(ring);
> When ringbuf_process_ring() returns an error, we need to use
> libbpf_err() to set the errno accordingly.

It seems that even when ringbuf_process_ring() returns a positive
result, we also need to cap it under INT_MAX, otherwise it may be cast
into a negative error.
>> +}
>> +
>> /* 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.
>
>
> .

2023-07-27 09:19:41

by Adam Sindelar

Subject: Re: [PATCH] libbpf: Expose API to consume one ring at a time

On Thu, Jul 27, 2023 at 02:17:12PM +0800, Hou Tao wrote:
> Hi,
>
> On 7/27/2023 9:06 AM, Hou Tao wrote:
> > Hi,
> >
> > On 7/26/2023 12:26 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]>
> >> ---
> >> tools/lib/bpf/libbpf.h | 1 +
> >> tools/lib/bpf/ringbuf.c | 15 +++++++++++++++
> >> 2 files changed, 16 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/ringbuf.c b/tools/lib/bpf/ringbuf.c
> >> index 02199364db136..8d087bfc7d005 100644
> >> --- a/tools/lib/bpf/ringbuf.c
> >> +++ b/tools/lib/bpf/ringbuf.c
> >> @@ -290,6 +290,21 @@ 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;
> >> +
> >> + if (ring_id >= rb->ring_cnt)
> >> + return libbpf_err(-EINVAL);
> >> +
> >> + ring = &rb->rings[ring_id];
> >> + return ringbuf_process_ring(ring);
> > When ringbuf_process_ring() returns an error, we need to use
> > libbpf_err() to set the errno accordingly.
>
> It seems that even when ringbuf_process_ring() returns a positive
> result, we also need to cap it under INT_MAX, otherwise it may be cast
> into a negative error.

Ah, sorry I missed that. Fixed in v3, going out in a few moments.

> >> +}
> >> +
> >> /* 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.
> >
> >
> > .
>

Thanks!