On 05/04/2018 03:37 AM, Jakub Kicinski wrote:
> Users of BPF sooner or later discover perf_event_output() helpers
> and BPF_MAP_TYPE_PERF_EVENT_ARRAY. Dumping this array type is
> not possible, however, we can add simple reading of perf events.
> Create a new event_pipe subcommand for maps, this sub command
> will only work with BPF_MAP_TYPE_PERF_EVENT_ARRAY maps.
>
> Parts of the code from samples/bpf/trace_output_user.c.
>
> Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
> Reviewed-by: Quentin Monnet <quentin.mon...@netronome.com>
[...]
One remark below:
[...]
> +static void
> +print_bpf_output(struct event_ring_info *ring, struct perf_event_sample *e)
> +{
> + struct {
> + struct perf_event_header header;
> + __u64 id;
> + __u64 lost;
> + } *lost = (void *)e;
> + struct timespec ts;
> +
> + if (clock_gettime(CLOCK_MONOTONIC, &ts)) {
> + perror("Can't read clock for timestamp");
> + return;
> + }
Instead of the timestamp above, probably better to pick it up via
PERF_SAMPLE_TIME which needs to be added to sample_type so it also
ends up in the RB. Given below you poll with 200 and you don't set
a wakeup event for perf RB (it's probably fine not to here, but it
can be done based on watermark or events), the clock_gettime() will
be off compared to when it was actually put into the RB.
> + if (json_output) {
> + jsonw_start_object(json_wtr);
> + jsonw_name(json_wtr, "timestamp");
> + jsonw_uint(json_wtr, ts.tv_sec * 1000000000ull + ts.tv_nsec);
> + jsonw_name(json_wtr, "type");
> + jsonw_uint(json_wtr, e->header.type);
> + jsonw_name(json_wtr, "cpu");
> + jsonw_uint(json_wtr, ring->cpu);
> + jsonw_name(json_wtr, "index");
> + jsonw_uint(json_wtr, ring->key);
> + if (e->header.type == PERF_RECORD_SAMPLE) {
> + jsonw_name(json_wtr, "data");
> + print_data_json(e->data, e->size);
> + } else if (e->header.type == PERF_RECORD_LOST) {
> + jsonw_name(json_wtr, "lost");
> + jsonw_start_object(json_wtr);
> + jsonw_name(json_wtr, "id");
> + jsonw_uint(json_wtr, lost->id);
> + jsonw_name(json_wtr, "count");
> + jsonw_uint(json_wtr, lost->lost);
> + jsonw_end_object(json_wtr);
> + }
> + jsonw_end_object(json_wtr);
> + } else {
> + if (e->header.type == PERF_RECORD_SAMPLE) {
> + printf("== @%ld.%ld CPU: %d index: %d =====\n",
> + (long)ts.tv_sec, ts.tv_nsec,
> + ring->cpu, ring->key);
> + fprint_hex(stdout, e->data, e->size, " ");
> + printf("\n");
> + } else if (e->header.type == PERF_RECORD_LOST) {
> + printf("lost %lld events\n", lost->lost);
> + } else {
> + printf("unknown event type=%d size=%d\n",
> + e->header.type, e->header.size);
> + }
