tools: bpftool: use PERF_SAMPLE_TIME instead of reading the clock

Ask the kernel to include sample time in each even instead of
reading the clock.  This is also more accurate because our
clock reading was done when user space would dump the buffer,
not when sample was produced.

Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/bpf/bpftool/map_perf_ring.c b/tools/bpf/bpftool/map_perf_ring.c
index c5a2ced8552d6e6971c019cbedb7e4dd1ea90a4e..9ae4bb8a2cadb59010881d2c2fb2a4ce1603d196 100644 (file)
--- a/tools/bpf/bpftool/map_perf_ring.c
+++ b/tools/bpf/bpftool/map_perf_ring.c
@@ -39,6 +39,7 @@ struct event_ring_info {
 
 struct perf_event_sample {
        struct perf_event_header header;
+       u64 time;
        __u32 size;
        unsigned char data[];
 };
@@ -57,17 +58,9 @@ print_bpf_output(struct event_ring_info *ring, struct perf_event_sample *e)
                __u64 id;
                __u64 lost;
        } *lost = (void *)e;
-       struct timespec ts;
-
-       if (clock_gettime(CLOCK_MONOTONIC, &ts)) {
-               perror("Can't read clock for timestamp");
-               return;
-       }
 
        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");
@@ -75,6 +68,8 @@ print_bpf_output(struct event_ring_info *ring, struct perf_event_sample *e)
                jsonw_name(json_wtr, "index");
                jsonw_uint(json_wtr, ring->key);
                if (e->header.type == PERF_RECORD_SAMPLE) {
+                       jsonw_name(json_wtr, "timestamp");
+                       jsonw_uint(json_wtr, e->time);
                        jsonw_name(json_wtr, "data");
                        print_data_json(e->data, e->size);
                } else if (e->header.type == PERF_RECORD_LOST) {
@@ -89,8 +84,8 @@ print_bpf_output(struct event_ring_info *ring, struct perf_event_sample *e)
                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,
+                       printf("== @%lld.%09lld CPU: %d index: %d =====\n",
+                              e->time / 1000000000ULL, e->time % 1000000000ULL,
                               ring->cpu, ring->key);
                        fprint_hex(stdout, e->data, e->size, " ");
                        printf("\n");
@@ -185,7 +180,7 @@ static void perf_event_unmap(void *mem)
 static int bpf_perf_event_open(int map_fd, int key, int cpu)
 {
        struct perf_event_attr attr = {
-               .sample_type = PERF_SAMPLE_RAW,
+               .sample_type = PERF_SAMPLE_RAW | PERF_SAMPLE_TIME,
                .type = PERF_TYPE_SOFTWARE,
                .config = PERF_COUNT_SW_BPF_OUTPUT,
        };