[PATCH] perf tools: Add hint for 'Too many events are opened.' error message

[Jiri Olsa <jolsa@kernel.org>]

Enhancing the 'Too many events are opened.' error message
with hint to use use 'ulimit -n <limit>' command.

Before:
  $ perf record -e 'sched:*,syscalls:*' ls
  Error:
  Too many events are opened.
  Try again after reducing the number of events.

Now:
  $ perf record -e 'sched:*,syscalls:*' ls
  Error:
  Too many events are opened.
  Probably the maximum number of open file descriptors has been reached.
  Hint: Try again after reducing the number of events.
  Hint: Try increasing the limit with 'ulimit -n <limit>'

Cc: Michael Petlan <mpetlan@redhat.com>
Link: http://lkml.kernel.org/n/tip-vfe0a2oxr4ga4ipl3nd90vk6@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/perf/util/evsel.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index c886b9f7a48d..a3e36fc634dc 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2149,7 +2149,9 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
 	case EMFILE:
 		return scnprintf(msg, size, "%s",
 			 "Too many events are opened.\n"
-			 "Try again after reducing the number of events.");
+			 "Probably the maximum number of open file descriptors has been reached.\n"
+			 "Hint: Try again after reducing the number of events.\n"
+			 "Hint: Try increasing the limit with 'ulimit -n <limit>'");
 	case ENODEV:
 		if (target->cpu_list)
 			return scnprintf(msg, size, "%s",
-- 
1.9.3