perf evsel: Inform how to make a sysctl setting permanent

When a tool can't open counters due to the kernel.perf_event_paranoit
sysctl setting, we inform how to tweak it to allow the operation to
succeed, in addition to that, suggest setting /etc/sysctl.conf to
make the setting permanent.

Suggested-by: Ingo Molnar <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: acmel

tools/perf/builtin-record.c

@@ -418,7 +418,7 @@ static int record__mmap(struct record *rec)
 
 static int record__open(struct record *rec)
 {
-	char msg[512];
+	char msg[BUFSIZ];
 	struct perf_evsel *pos;
 	struct perf_evlist *evlist = rec->evlist;
 	struct perf_session *session = rec->session;

tools/perf/builtin-stat.c

@@ -533,7 +533,7 @@ static int store_counter_ids(struct perf_evsel *counter)
 static int __run_perf_stat(int argc, const char **argv)
 {
 	int interval = stat_config.interval;
-	char msg[512];
+	char msg[BUFSIZ];
 	unsigned long long t0, t1;
 	struct perf_evsel *counter;
 	struct timespec ts;

tools/perf/builtin-top.c

@@ -859,7 +859,7 @@ static void perf_top__mmap_read(struct perf_top *top)
 
 static int perf_top__start_counters(struct perf_top *top)
 {
-	char msg[512];
+	char msg[BUFSIZ];
 	struct perf_evsel *counter;
 	struct perf_evlist *evlist = top->evlist;
 	struct record_opts *opts = &top->record_opts;

tools/perf/util/evsel.c

@@ -2469,7 +2469,9 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
 		 "  -1: Allow use of (almost) all events by all users\n"
 		 ">= 0: Disallow raw tracepoint access by users without CAP_IOC_LOCK\n"
 		 ">= 1: Disallow CPU event access by users without CAP_SYS_ADMIN\n"
-		 ">= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN",
+		 ">= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN\n\n"
+		 "To make this setting permanent, edit /etc/sysctl.conf too, e.g.:\n\n"
+		 "	kernel.perf_event_paranoid = -1\n" ,
 				 target->system_wide ? "system-wide " : "",
 				 perf_event_paranoid());
 	case ENOENT: