[PATCH v1] perf evlist: Warn when 'sleep' workload is used without system-wide (-a) option

[Ian Rogers <irogers@google.com>]

A common mistake when trying to record system-wide profiles for a given
duration is running commands like 'perf record sleep 1' or 'perf stat
sleep 1' without passing '-a' / '--all-cpus'. When '-a' is omitted, perf
defaults to per-process monitoring of the sleep process itself, which
does not collect system-wide activity and records very few events.

Add a warning in evlist__prepare_workload() when the workload executable
is 'sleep' and system-wide mode is not enabled.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/evlist.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index eb7c0d7be064..d53f594ace86 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -1562,6 +1562,20 @@ int evlist__prepare_workload(struct evlist *evlist, struct target *target, const
 	int child_ready_pipe[2], go_pipe[2];
 	char bf;
 
+	if (argv && argv[0] && target && !target->system_wide) {
+		const char *cmd = strrchr(argv[0], '/');
+
+		if (cmd)
+			cmd++;
+		else
+			cmd = argv[0];
+
+		if (!strcmp(cmd, "sleep")) {
+			ui__warning("workload '%s' specified without the system-wide (-a) option\n",
+				    cmd);
+		}
+	}
+
 	evlist__set_workload_cork_fd(evlist, -1);
 
 	if (pipe(child_ready_pipe) < 0) {
-- 
2.55.0.629.g250fe7f194-goog