[PATCH] perf/test: fix perf ftrace test on s390

[Thomas Richter <tmricht@linux.ibm.com>]

On s390 the perf test case ftrace sometimes fails as follows:

  # ./perf test ftrace
  79: perf ftrace tests    : FAILED!
  #

The failure depends on the kernel .config file. Some configurarions
always work fine, some do not.
To achieve success for all our tested kernel configurations, enlarge
the buffer to store the traces complete without wrapping.
The default buffer size is too small  for all kernel configurations.
Set the buffer size of /sys/kernel/tracing/buffer_size_kb to 16 MB

Output after:
  # ./perf test ftrace
  79: perf ftrace tests     : Ok
  #

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Suggested-by: Sven Schnelle <svens@linux.ibm.com>
---
 tools/perf/tests/shell/ftrace.sh | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/perf/tests/shell/ftrace.sh b/tools/perf/tests/shell/ftrace.sh
index a6ee740f0d7e..742d6b8f34d3 100755
--- a/tools/perf/tests/shell/ftrace.sh
+++ b/tools/perf/tests/shell/ftrace.sh
@@ -80,10 +80,21 @@ test_ftrace_profile() {
     echo "perf ftrace profile test  [Success]"
 }
 
+if [ "$(uname -m)" = "s390x" ]
+then
+	ftrace_size=$(cat /sys/kernel/tracing/buffer_size_kb)
+	echo 16384 > /sys/kernel/tracing/buffer_size_kb
+fi
+
 test_ftrace_list
 test_ftrace_trace
 test_ftrace_latency
 test_ftrace_profile
 
+if [ "$(uname -m)" = "s390x" ]
+then
+	echo $ftrace_size > /sys/kernel/tracing/buffer_size_kb
+fi
+
 cleanup
 exit 0
-- 
2.47.0