[PATCH 2/3] perf: builtin-record: Provide advice if mmap'ing fails with EPERM.

[Nelson Elhage]

This failure is most likely due to running up against the
kernel.perf_event_mlock_kb sysctl, so we can tell the user what to do
to fix the issue.

Signed-off-by: Nelson Elhage <nelhage@xxxxxxxxxxx>
---
 tools/perf/builtin-record.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 6ab58cc..45b23c1 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -358,8 +358,15 @@ try_again:
 		exit(-1);
 	}
 
-	if (perf_evlist__mmap(evlist, mmap_pages, false) < 0)
+	if (perf_evlist__mmap(evlist, mmap_pages, false) < 0) {
+		if (errno == EPERM)
+			die("Permission error mapping pages.\n"
+			    "Consider increasing "
+			    "/proc/sys/kernel/perf_event_mlock_kb,\n"
+			    "or try again with a smaller value of -m/--mmap_pages.\n"
+			    "(current value: %d)\n", mmap_pages);
 		die("failed to mmap with %d (%s)\n", errno, strerror(errno));
+	}
 
 	if (file_new)
 		session->evlist = evlist;
-- 
1.7.4.41.g50b8f

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