On Mon, May 25, 2020 at 2:01 PM Eelco Chaudron <echaudro@xxxxxxxxxx> wrote:
>
> This new API, perf_buffer__consume, can be used as follows:
I wonder, was it inspired by yet-to-be committed
ring_buffer__consume() or it's just a coincidence?
> - When you have a perf ring where wakeup_events is higher than 1,
> and you have remaining data in the rings you would like to pull
> out on exit (or maybe based on a timeout).
> - For low latency cases where you burn a CPU that constantly polls
> the queues.
>
> Signed-off-by: Eelco Chaudron <echaudro@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 23 +++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 1 +
> tools/lib/bpf/libbpf.map | 1 +
> 3 files changed, 25 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index fa04cbe547ed..cbef3dac7507 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -8456,6 +8456,29 @@ int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms)
> return cnt < 0 ? -errno : cnt;
> }
>
> +int perf_buffer__consume(struct perf_buffer *pb)
> +{
> + int i;
> +
> + if (!pb)
> + return -EINVAL;
we don't check this in perf_buffer__poll, IMO, checking this in every
"method" is an overkill.
> +
> + if (!pb->cpu_bufs)
> + return 0;
no need to check. It's either non-NULL for valid perf_buffer, or
calloc could return NULL if pb->cpu_cnt is zero (not sure it's
possible, but still), but then loop below will never access
pb->cpu_bufs[i].
> +
> + for (i = 0; i < pb->cpu_cnt && pb->cpu_bufs[i]; i++) {
I think pb->cpu_bufs[i] check is wrong, it will stop iteration
prematurely if cpu_bufs are sparsely populated. So move check inside
and continue loop if NULL.
> + int err;
nit: declare it together with "i" above, similar to how
perf_buffer__poll does it
> + struct perf_cpu_buf *cpu_buf = pb->cpu_bufs[i];
> +
> + err = perf_buffer__process_records(pb, cpu_buf);
> + if (err) {
> + pr_warn("error while processing records: %d\n", err);
> + return err;
> + }
> + }
> + return 0;
> +}
> +
> struct bpf_prog_info_array_desc {
> int array_offset; /* e.g. offset of jited_prog_insns */
> int count_offset; /* e.g. offset of jited_prog_len */
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 8ea69558f0a8..1e2e399a5f2c 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -533,6 +533,7 @@ perf_buffer__new_raw(int map_fd, size_t page_cnt,
>
> LIBBPF_API void perf_buffer__free(struct perf_buffer *pb);
> LIBBPF_API int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms);
> +LIBBPF_API int perf_buffer__consume(struct perf_buffer *pb);
>
> typedef enum bpf_perf_event_ret
> (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 0133d469d30b..381a7342ecfc 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -262,4 +262,5 @@ LIBBPF_0.0.9 {
> bpf_link_get_fd_by_id;
> bpf_link_get_next_id;
> bpf_program__attach_iter;
> + perf_buffer__consume;
> } LIBBPF_0.0.8;
>
