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 <mingo@kernel.org>
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-4gwe99k4a6p12d4u8bbyttj2@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

4 files changed, 6 insertions, 4 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index ffac8ca9fb01..2ddf189968dc 100644
--- a/tools/perf/builtin-record.c
+++ b/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;
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index a02f2e965628..f28719178b51 100644
--- a/tools/perf/builtin-stat.c
+++ b/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;
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index d90927f31ff6..5a7fd7af3a6d 100644
--- a/tools/perf/builtin-top.c
+++ b/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;
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 04e536ae4d88..cd2fb42e5dd4 100644
--- a/tools/perf/util/evsel.c
+++ b/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: