From 43375e6bbe389606fbd24d0a84535285a1a8040c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Lyson=C4=9Bk?= <olysonek@redhat.com>
Date: Thu, 17 Sep 2020 18:57:24 +0800
Subject: [PATCH] cpu: Update checking if EPB is supported

Update checking if EPB is supported so that it works with recent
versions of the x86_energy_perf_policy tool. Newer versions of
x86_energy_perf_policy, unlike older versions, exit with a zero exit
code even if the CPU doesn't support EPB. Newer versions of the tool
give no ouput on stdout if EPB is not supported, so check for that.

In the future, we might like to determine if EPB is supported by
searching /proc/cpuinfo for specific CPU flags. However the solution
described in the previous paragraph should work just fine for now.

Resolves: rhbz#1690929

Signed-off-by: Ondřej Lysoněk <olysonek@redhat.com>

https://github.com/redhat-performance/tuned/pull/217/commits/43375e6bbe389606fbd24d0a84535285a1a8040c
---
 tuned/plugins/plugin_cpu.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tuned/plugins/plugin_cpu.py b/tuned/plugins/plugin_cpu.py
index 8f0babd..4934022 100644
--- a/tuned/plugins/plugin_cpu.py
+++ b/tuned/plugins/plugin_cpu.py
@@ -61,8 +61,11 @@ class CPULatencyPlugin(base.Plugin):
 	def _check_energy_perf_bias(self):
 		self._has_energy_perf_bias = False
 		retcode_unsupported = 1
-		retcode = self._cmd.execute(["x86_energy_perf_policy", "-r"], no_errors = [errno.ENOENT, retcode_unsupported])[0]
-		if retcode == 0:
+		retcode, out = self._cmd.execute(["x86_energy_perf_policy", "-r"], no_errors = [errno.ENOENT, retcode_unsupported])
+               # With recent versions of the tool, a zero exit code is
+               # returned even if EPB is not supported. The output is empty
+               # in that case, however.
+		if retcode == 0 and out != "":
 			self._has_energy_perf_bias = True
 		elif retcode < 0:
 			log.warning("unable to run x86_energy_perf_policy tool, ignoring CPU energy performance bias, is the tool installed?")
-- 
2.23.0