perf: builtin-record: Provide advice if mmap'ing fails with EPERM.

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.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1324301972-22740-3-git-send-email-nelhage@nelhage.com
Signed-off-by: Nelson Elhage <nelhage@nelhage.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -272,8 +272,15 @@ try_again:
 		exit(-1);
 	}
 
-	if (perf_evlist__mmap(evlist, opts->mmap_pages, false) < 0)
+	if (perf_evlist__mmap(evlist, opts->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", opts->mmap_pages);
 		die("failed to mmap with %d (%s)\n", errno, strerror(errno));
+	}
 
 	if (rec->file_new)
 		session->evlist = evlist;