On 26 May 2020, at 7:29, Andrii Nakryiko wrote:
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?
Just coincidence, I was needing a function to flush the remaining ring
entries, as I was using a larger wakeup_events value.
Initially, I called the function ring_buffer_flush(), but once I noticed
your patch I renamed it :)
- 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.
Ack, will fix in v2
+
+ 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].
Agreed, was just adding some safety checks, but in the constantly poll
mode this is a lot of overhead. Will remover in v2.
+
+ 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.
Mimicked the behavior from other functions, however just to be safe I
split it up.
+ int err;
nit: declare it together with "i" above, similar to how
perf_buffer__poll does it
Put it down here as it’s only used in the context of the for loop, but
will move it up in the v2.
+ 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;
Thanks for the review, will send out a v2 soon.
