oeqa.buildperf: functionality to drop kernel caches

Add a new utility class for dropping Linux kernel caches.  It uses sudo
and tee to write to the drop_caches file. Checking if the user has the
permissions to drop caches (without a password) is done by trying to
writing an invalid value to the drop_caches file. This way, we will find
if writing (with tee) is possible but not really dropping caches, yet.

User can avoid giving the password by adding something like:
<user> ALL = NOPASSWD: /usr/bin/tee /proc/sys/vm/drop_caches
to the system sudoers file.

(From OE-Core rev: c9cb248429ced50c96d11ba5361c272d4c9b9323)

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/buildperf/__init__.py

@@ -10,3 +10,4 @@
 # more details.
 #
 """Build performance tests"""
+from .base import KernelDropCaches

meta/lib/oeqa/buildperf/base.py

@@ -0,0 +1,46 @@
+# Copyright (c) 2016, Intel Corporation.
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms and conditions of the GNU General Public License,
+# version 2, as published by the Free Software Foundation.
+#
+# This program is distributed in the hope it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+# more details.
+#
+"""Build performance test base classes and functionality"""
+from oeqa.utils.commands import runCmd
+
+
+class KernelDropCaches(object):
+    """Container of the functions for dropping kernel caches"""
+    sudo_passwd = None
+
+    @classmethod
+    def check(cls):
+        """Check permssions for dropping kernel caches"""
+        from getpass import getpass
+        from locale import getdefaultlocale
+        cmd = ['sudo', '-k', '-n', 'tee', '/proc/sys/vm/drop_caches']
+        ret = runCmd(cmd, ignore_status=True, data=b'0')
+        if ret.output.startswith('sudo:'):
+            pass_str = getpass(
+                "\nThe script requires sudo access to drop caches between "
+                "builds (echo 3 > /proc/sys/vm/drop_caches).\n"
+                "Please enter your sudo password: ")
+            cls.sudo_passwd = bytes(pass_str, getdefaultlocale()[1])
+
+    @classmethod
+    def drop(cls):
+        """Drop kernel caches"""
+        cmd = ['sudo', '-k']
+        if cls.sudo_passwd:
+            cmd.append('-S')
+            input_data = cls.sudo_passwd + b'\n'
+        else:
+            cmd.append('-n')
+            input_data = b''
+        cmd += ['tee', '/proc/sys/vm/drop_caches']
+        input_data += b'3'
+        runCmd(cmd, data=input_data)

scripts/oe-build-perf-test

@@ -22,6 +22,7 @@ import sys
 sys.path.insert(0, os.path.dirname(os.path.realpath(__file__)) + '/lib')
 import scriptpath
 scriptpath.add_oe_lib_path()
+from oeqa.buildperf import KernelDropCaches
 from oeqa.utils.commands import runCmd
 
 
@@ -71,6 +72,9 @@ def main(argv=None):
     if not pre_run_sanity_check():
         return 1
 
+    # Check our capability to drop caches and ask pass if needed
+    KernelDropCaches.check()
+
     return 0