perf script: Support relative time

When comparing time stamps in 'perf script' traces it can be annoying to
work with the full perf time stamps.

Add a --reltime option that displays time stamps relative to the trace
start to make it easier to read the traces.

Note: not currently supported for --time. Report an error in this
case.

Before:

  % perf script
      swapper 0 [000] 245402.891216:    1 cycles:ppp: ffffffffa0068814 native_write_msr+0x4 ([kernel.kallsyms])
      swapper 0 [000] 245402.891223:    1 cycles:ppp: ffffffffa0068814 native_write_msr+0x4 ([kernel.kallsyms])
      swapper 0 [000] 245402.891227:    5 cycles:ppp: ffffffffa0068814 native_write_msr+0x4 ([kernel.kallsyms])
      swapper 0 [000] 245402.891231:   41 cycles:ppp: ffffffffa0068816 native_write_msr+0x6 ([kernel.kallsyms])
      swapper 0 [000] 245402.891235:  355 cycles:ppp: ffffffffa000dd51 intel_bts_enable_local+0x21 ([kernel.kallsyms])
      swapper 0 [000] 245402.891239: 3084 cycles:ppp: ffffffffa0a0150a end_repeat_nmi+0x48 ([kernel.kallsyms])

After:

  % perf script --reltime

      swapper 0 [000]     0.000000:    1 cycles:ppp: ffffffffa0068814 native_write_msr+0x4 ([kernel.kallsyms])
      swapper 0 [000]     0.000006:    1 cycles:ppp: ffffffffa0068814 native_write_msr+0x4 ([kernel.kallsyms])
      swapper 0 [000]     0.000010:    5 cycles:ppp: ffffffffa0068814 native_write_msr+0x4 ([kernel.kallsyms])
      swapper 0 [000]     0.000014:   41 cycles:ppp: ffffffffa0068816 native_write_msr+0x6 ([kernel.kallsyms])
      swapper 0 [000]     0.000018:  355 cycles:ppp: ffffffffa000dd51 intel_bts_enable_local+0x21 ([kernel.kallsyms])
      swapper 0 [000]     0.000022: 3084 cycles:ppp: ffffffffa0a0150a end_repeat_nmi+0x48 ([kernel.kallsyms])

Committer notes:

Do not use 'time' as the name of a variable, as this breaks the build on
older glibcs:

  cc1: warnings being treated as errors
  builtin-script.c: In function 'perf_sample__fprintf_start':
  builtin-script.c:691: warning: declaration of 'time' shadows a global declaration
  /usr/include/time.h:187: warning: shadowed declaration is here
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
LPU-Reference: 20190314225002.30108-8-andi@firstfloor.org
Link: https://lkml.kernel.org/n/tip-bpahyi6pr9r399mvihu65fvc@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-script.txt

@@ -380,6 +380,9 @@ include::itrace.txt[]
 	Set the maximum number of program blocks to print with brstackasm for
 	each sample.
 
+--reltime::
+	Print time stamps relative to trace start.
+
 --per-event-dump::
 	Create per event files with a "perf.data.EVENT.dump" name instead of
         printing to stdout, useful, for instance, for generating flamegraphs.

tools/perf/builtin-script.c

@@ -53,6 +53,8 @@
 
 static char const		*script_name;
 static char const		*generate_script_lang;
+static bool			reltime;
+static u64			initial_time;
 static bool			debug_mode;
 static u64			last_timestamp;
 static u64			nr_unordered;
@@ -686,7 +688,13 @@ static int perf_sample__fprintf_start(struct perf_sample *sample,
 	}
 
 	if (PRINT_FIELD(TIME)) {
-		nsecs = sample->time;
+		u64 t = sample->time;
+		if (reltime) {
+			if (!initial_time)
+				initial_time = sample->time;
+			t = sample->time - initial_time;
+		}
+		nsecs = t;
 		secs = nsecs / NSEC_PER_SEC;
 		nsecs -= secs * NSEC_PER_SEC;
 
@@ -694,7 +702,7 @@ static int perf_sample__fprintf_start(struct perf_sample *sample,
 			printed += fprintf(fp, "%5lu.%09llu: ", secs, nsecs);
 		else {
 			char sample_time[32];
-			timestamp__scnprintf_usec(sample->time, sample_time, sizeof(sample_time));
+			timestamp__scnprintf_usec(t, sample_time, sizeof(sample_time));
 			printed += fprintf(fp, "%12s: ", sample_time);
 		}
 	}
@@ -3413,6 +3421,7 @@ int cmd_script(int argc, const char **argv)
 		     "Set the maximum stack depth when parsing the callchain, "
 		     "anything beyond the specified depth will be ignored. "
 		     "Default: kernel.perf_event_max_stack or " __stringify(PERF_MAX_STACK_DEPTH)),
+	OPT_BOOLEAN(0, "reltime", &reltime, "Show time stamps relative to start"),
 	OPT_BOOLEAN('I', "show-info", &show_full_info,
 		    "display extended information from perf.data file"),
 	OPT_BOOLEAN('\0', "show-kernel-path", &symbol_conf.show_kernel_path,
@@ -3487,6 +3496,11 @@ int cmd_script(int argc, const char **argv)
 		}
 	}
 
+	if (script.time_str && reltime) {
+		fprintf(stderr, "Don't combine --reltime with --time\n");
+		return -1;
+	}
+
 	if (itrace_synth_opts.callchain &&
 	    itrace_synth_opts.callchain_sz > scripting_max_stack)
 		scripting_max_stack = itrace_synth_opts.callchain_sz;