perf auxtrace: Add Z itrace option for timeless decoding

Issues correlating timestamps can be avoided with timeless decoding. Add
an option for that, so that timeless decoding can be used even when
timestamps are present.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210430070309.17624-2-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/itrace.txt

@@ -20,6 +20,7 @@
 		L	synthesize last branch entries on existing event records
 		s       skip initial number of events
 		q	quicker (less detailed) decoding
+		Z	prefer to ignore timestamps (so-called "timeless" decoding)
 
 	The default is all events i.e. the same as --itrace=ibxwpe,
 	except for perf script where it is --itrace=ce

tools/perf/util/auxtrace.c

@@ -1569,6 +1569,9 @@ int itrace_parse_synth_opts(const struct option *opt, const char *str,
 		case 'q':
 			synth_opts->quick += 1;
 			break;
+		case 'Z':
+			synth_opts->timeless_decoding = true;
+			break;
 		case ' ':
 		case ',':
 			break;

tools/perf/util/auxtrace.h

@@ -89,6 +89,7 @@ enum itrace_period_type {
  * @tlb: whether to synthesize TLB events
  * @remote_access: whether to synthesize remote access events
  * @mem: whether to synthesize memory events
+ * @timeless_decoding: prefer "timeless" decoding i.e. ignore timestamps
  * @callchain_sz: maximum callchain size
  * @last_branch_sz: branch context size
  * @period: 'instructions' events period
@@ -128,6 +129,7 @@ struct itrace_synth_opts {
 	bool			tlb;
 	bool			remote_access;
 	bool			mem;
+	bool			timeless_decoding;
 	unsigned int		callchain_sz;
 	unsigned int		last_branch_sz;
 	unsigned long long	period;