From: Jakub Kicinski <jakub.kicinski@netronome.com>
Date: Thu, 10 May 2018 10:24:37 -0700
Subject: tools: bpftool: use PERF_SAMPLE_TIME instead of reading the clock
Patch-mainline: v4.18-rc1
Git-commit: e3687510fce2a5b039133be8979b2c8e8cbffa67
References: bsc#1109837

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>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 tools/bpf/bpftool/map_perf_ring.c |   17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

--- 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
 		__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
 		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
 		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,
 	};