[PATCH 1/2] perf tools: Add reference timestamp to perf header

[David Ahern]

Add a reference timestamp to the perf header - snapshotting kernel
time to gettimeofday. This allows 'perf report' to convert kernel
timestamps to time-of-day which is convenient for comparing to other
(non perf related) log files.

The timestamp is added using a feature bit for compatibility with
older binaries and data files.

Signed-off-by: David Ahern <daahern@xxxxxxxxx>
---
 tools/perf/util/header.c  |   51 +++++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/header.h  |    3 ++
 tools/perf/util/session.c |   26 +++++++++++++++++++++++
 3 files changed, 80 insertions(+), 0 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 76e949a..2fe893b 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -191,6 +191,40 @@ static int write_padded(int fd, const void *bf, size_t count,
 	return err;
 }
 
+static int perf_header__read_ref_time(struct perf_header *header,
+			int fd, u64 offset, u64 size)
+{
+	size_t sz_nsec = sizeof(header->nsec_ref);
+	size_t sz_tv   = sizeof(header->tv_ref);
+	int err = -1;
+
+	if (((size - offset) < (sz_nsec + sz_tv)) ||
+	    (read(fd, &header->nsec_ref, sz_nsec) != (ssize_t) sz_nsec) ||
+	    (read(fd, &header->tv_ref, sz_tv) != (ssize_t) sz_tv))
+		goto out;
+
+	err = 0;
+
+out:
+	return err;
+}
+
+static int perf_header__write_ref_time(struct perf_header *header, int fd)
+{
+	size_t sz_nsec = sizeof(header->nsec_ref);
+	size_t sz_tv   = sizeof(header->tv_ref);
+	int err = -1;
+
+	if ((write(fd, &header->nsec_ref, sz_nsec) != (ssize_t) sz_nsec) ||
+	    (write(fd, &header->tv_ref, sz_tv) != (ssize_t) sz_tv))
+		goto out;
+
+	err = 0;
+
+out:
+	return err;
+}
+
 #define dsos__for_each_with_build_id(pos, head)	\
 	list_for_each_entry(pos, head, node)	\
 		if (!pos->has_build_id)		\
@@ -483,6 +517,19 @@ static int perf_header__adds_write(struct perf_header *self, int fd)
 			perf_session__cache_build_ids(session);
 	}
 
+	if (perf_header__has_feat(self, HEADER_REFERENCE_TIME)) {
+		struct perf_file_section *tref_sec;
+
+		tref_sec = &feat_sec[idx++];
+		tref_sec->offset = lseek(fd, 0, SEEK_CUR);
+		err = perf_header__write_ref_time(self, fd);
+		if (err < 0) {
+			pr_debug("failed to write reference time\n");
+			goto out_free;
+		}
+		tref_sec->size = lseek(fd, 0, SEEK_CUR) - tref_sec->offset;
+	}
+
 	lseek(fd, sec_start, SEEK_SET);
 	err = do_write(fd, feat_sec, sec_size);
 	if (err < 0)
@@ -810,6 +857,10 @@ static int perf_file_section__process(struct perf_file_section *self,
 		if (perf_header__read_build_ids(ph, fd, self->offset, self->size))
 			pr_debug("Failed to read buildids, continuing...\n");
 		break;
+	case HEADER_REFERENCE_TIME:
+		if (perf_header__read_ref_time(ph, fd, self->offset, self->size))
+			pr_debug("Failed to read reference time, continuing...\n");
+		break;
 	default:
 		pr_debug("unknown feature %d, continuing...\n", feat);
 	}
diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
index 6335965..0721c78 100644
--- a/tools/perf/util/header.h
+++ b/tools/perf/util/header.h
@@ -19,6 +19,7 @@ struct perf_header_attr {
 enum {
 	HEADER_TRACE_INFO = 1,
 	HEADER_BUILD_ID,
+	HEADER_REFERENCE_TIME,
 	HEADER_LAST_FEATURE,
 };
 
@@ -59,6 +60,8 @@ struct perf_header {
 	u64			data_size;
 	u64			event_offset;
 	u64			event_size;
+	u64			nsec_ref;
+	struct timeval		tv_ref;
 	DECLARE_BITMAP(adds_features, HEADER_FEAT_BITS);
 };
 
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 3074d38..720838e 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -110,6 +110,29 @@ void perf_session__update_sample_type(struct perf_session *self)
 	perf_session__id_header_size(self);
 }
 
+static int perf_session__create_ref_time(struct perf_session *session)
+{
+	struct timespec tp;
+
+	/* race here between successive calls, but should be close enough */
+	if (gettimeofday(&session->header.tv_ref, NULL) != 0) {
+		pr_err("gettimeofday failed. Cannot set reference time.\n");
+		return -1;
+	}
+
+	if (clock_gettime(CLOCK_MONOTONIC, &tp) != 0) {
+		pr_err("clock_gettime failed. Cannot set reference time.\n");
+		return -1;
+	}
+
+	session->header.nsec_ref = (u64) tp.tv_sec * NSEC_PER_SEC
+		                       + (u64) tp.tv_nsec;
+
+	perf_header__set_feat(&session->header, HEADER_REFERENCE_TIME);
+
+	return 0;
+}
+
 int perf_session__create_kernel_maps(struct perf_session *self)
 {
 	int ret = machine__create_kernel_maps(&self->host_machine);
@@ -167,6 +190,9 @@ struct perf_session *perf_session__new(const char *filename, int mode, bool forc
 		 */
 		if (perf_session__create_kernel_maps(self) < 0)
 			goto out_delete;
+
+		if (perf_session__create_ref_time(self) < 0)
+			goto out_delete;
 	}
 
 	perf_session__update_sample_type(self);
-- 
1.7.2.3

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