perf evsel: State in the default event name if attr.exclude_kernel is set

When no event is specified perf will use the "cycles" hardware event
with the highest precision available in the processor, and excluding
kernel events for non-root users, so make that clear in the event name
by setting the "u" event modifier, i.e. "cycles:upp".

E.g.:

The default for root:

  # perf record usleep 1
  # perf evlist -v
  cycles:ppp: ..., precise_ip: 3, exclude_kernel: 0, ...
  #

And for !root:

  $ perf record usleep 1
  $ perf evlist -v
  cycles:uppp: ... , precise_ip: 3, exclude_kernel: 1, ...
  $

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-lf29zcdl422i9knrgde0uwy3@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -298,8 +298,10 @@ struct perf_evsel *perf_evsel__new_cycles(void)
 		goto out;
 
 	/* use asprintf() because free(evsel) assumes name is allocated */
-	if (asprintf(&evsel->name, "cycles%.*s",
-		     attr.precise_ip ? attr.precise_ip + 1 : 0, ":ppp") < 0)
+	if (asprintf(&evsel->name, "cycles%s%s%.*s",
+		     (attr.precise_ip || attr.exclude_kernel) ? ":" : "",
+		     attr.exclude_kernel ? "u" : "",
+		     attr.precise_ip ? attr.precise_ip + 1 : 0, "ppp") < 0)
 		goto error_free;
 out:
 	return evsel;