perf trace: Allow configuring if the syscall start timestamp should be printed

# trace -e open*,close,*sleep sleep 1
0.000 openat(dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC ) = 3
0.016 close(fd: 3 ) = 0
0.024 openat(dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC ) = 3
0.074 close(fd: 3 ) = 0
0.235 openat(dfd: CWD, filename: /usr/lib/locale/locale-archive, flags: CLOEXEC) = 3
0.251 close(fd: 3 ) = 0
0.285 nanosleep(rqtp: 0x7ffd68e6d620, rmtp: 0 ) = 0
1000.386 close(fd: 1 ) = 0
1000.395 close(fd: 2 ) = 0
#

# perf config trace.show_timestamp=no
# trace -e open*,close,*sleep sleep 1
openat(dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC ) = 3
close(fd: 3 ) = 0
openat(dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC ) = 3
close(fd: 3 ) = 0
openat(dfd: CWD, filename: , flags: CLOEXEC ) = 3
close(fd: 3 ) = 0
nanosleep(rqtp: 0x7fffa79c38e0, rmtp: 0 ) = 0
close(fd: 1 ) = 0
close(fd: 2 ) = 0
#

Cc: Adrian Hunter <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Luis Cláudio Gonçalves <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: https://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-config.txt

···
 	trace.show_duration::
 		Show syscall duration.
 
+	trace.show_timestamp::
+		Show syscall start timestamp.
+
 	trace.show_zeros::
 		Do not suppress syscall arguments that are equal to zero.
 

tools/perf/builtin-trace.c

···
 	bool			show_tool_stats;
 	bool			trace_syscalls;
 	bool			kernel_syscallchains;
+	bool			show_tstamp;
 	bool			show_duration;
 	bool			show_zeros;
 	bool			force;
···
 static size_t trace__fprintf_entry_head(struct trace *trace, struct thread *thread,
 					u64 duration, bool duration_calculated, u64 tstamp, FILE *fp)
 {
-	size_t printed = trace__fprintf_tstamp(trace, tstamp, fp);
+	size_t printed = 0;
+
+	if (trace->show_tstamp)
+		printed = trace__fprintf_tstamp(trace, tstamp, fp);
 	if (trace->show_duration)
 		printed += fprintf_duration(duration, duration_calculated, fp);
 	return printed + trace__fprintf_comm_tid(trace, thread, fp);
···
 					       "event selector. use 'perf list' to list available events",
 					       parse_events_option);
 		err = parse_events_option(&o, value, 0);
+	} else if (!strcmp(var, "trace.show_timestamp")) {
+		trace->show_tstamp = perf_config_bool(var, value);
 	} else if (!strcmp(var, "trace.show_duration")) {
 		trace->show_duration = perf_config_bool(var, value);
 	} else if (!strcmp(var, "trace.show_zeros")) {
···
 		},
 		.output = stderr,
 		.show_comm = true,
+		.show_tstamp = true,
 		.show_duration = true,
 		.trace_syscalls = false,
 		.kernel_syscallchains = false,