[tip:perf/core] perf data: Document clockid header: HEADER_CLOCKID

[tip-bot for Arnaldo Carvalho de Melo]

Commit-ID:  a9de7cfc7663882e98ec3b2ecf35c546a013b956
Gitweb:     https://git.kernel.org/tip/a9de7cfc7663882e98ec3b2ecf35c546a013b956
Author:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
AuthorDate: Wed, 29 May 2019 15:43:51 -0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Wed, 5 Jun 2019 09:47:53 -0300

perf data: Document clockid header: HEADER_CLOCKID

We forgot to update the perf.data file format document for the
HEADER_CLOCKID header, do it now from comments in the patch introducing
it.

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Chong Jiang <chongjiang@xxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Simon Que <sque@xxxxxxxxxxxx>
Fixes: cf7905165fee ("perf record: Encode -k clockid frequency into Perf trace")
Link: https://lkml.kernel.org/n/tip-slhnjp06027j3ae17qqetzxj@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/Documentation/perf.data-file-format.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
index 99733751695b..600999f89c6d 100644
--- a/tools/perf/Documentation/perf.data-file-format.txt
+++ b/tools/perf/Documentation/perf.data-file-format.txt
@@ -296,6 +296,12 @@ $ perf report --header-only -I
 # memory nodes (nr 1, block size 0x8000000):
 #    0 [7G]: 0-23,32-69
 
+	HEADER_CLOCKID = 23,
+
+One uint64_t for the clockid frequency, specified, for instance, via 'perf
+record -k' (see clock_gettime()), to enable timestamps derived metrics
+conversion into wall clock time on the reporting stage.
+
         HEADER_BPF_PROG_INFO = 25,
 
 struct bpf_prog_info_linear, which contains detailed information about