From 1d1c3a389c393afa1e88d5629f5dff85824fc92b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jaroslav=20=C5=A0karvada?= <jskarvad@redhat.com>
Date: Wed, 7 May 2014 17:02:59 +0200
Subject: tuned: Added support for >, < assignment modifiers in tuned.conf
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These modifiers can specify when to assign new value considering
the old value.

E.g.:
readahead=>4096

means assign readahead 4096 only if the current value of readahaed
is lower than 4096 (i.e. the readahaed will be at least 4096).

Similarly for the < operator, it will assign the value only
if the current value is higher.

The modifiers are part of the value, not part of the equality
operator, thus the following is correct:
readahead= >4096

But the following isn't correct, but will probably also work
due to the nature how the value is parsed:
readahead=> 4096

Signed-off-by: Jaroslav Škarvada <jskarvad@redhat.com>

diff --git a/profiles/throughput-performance/tuned.conf b/profiles/throughput-performance/tuned.conf
index dae02dc..42473a9 100644
--- a/profiles/throughput-performance/tuned.conf
+++ b/profiles/throughput-performance/tuned.conf
@@ -11,7 +11,7 @@ min_perf_pct=100
 transparent_hugepages=always
 
 [disk]
-readahead=4096
+readahead=>4096
 
 [sysctl]
 # ktune sysctl settings for rhel6 servers, maximizing i/o throughput
diff --git a/tuned/plugins/base.py b/tuned/plugins/base.py
index bad487f..f0faf38 100644
--- a/tuned/plugins/base.py
+++ b/tuned/plugins/base.py
@@ -212,7 +212,7 @@ class Plugin(object):
 
 	def _instance_apply_dynamic(self, instance, device):
 		for option in filter(lambda opt: self._storage_get(instance, self._commands[opt], device) is None, self._options_used_by_dynamic):
-			self._save_current_value(instance, self._commands[option], device)
+			self._check_and_save_value(instance, self._commands[option], device)
 
 		self._instance_update_dynamic(instance, device)
 
@@ -317,27 +317,50 @@ class Plugin(object):
 			for device in devices:
 				self._execute_device_command(instance, command, device, new_value)
 
-	def _save_current_value(self, instance, command, device = None):
+	def _check_and_save_value(self, instance, command, device = None, new_value = None):
 		if device is not None:
 			current_value = command["get"](device)
 		else:
 			current_value = command["get"]()
+		if new_value is not None:
+			nws = str(new_value)
+			op = nws[:1]
+			val = nws[1:]
+			try:
+				if op == ">":
+					if int(val) > int(current_value):
+						new_value = val;
+					else:
+						current_value = None
+						new_value = None
+				elif op == "<":
+					if int(val) < int(current_value):
+						new_value = val;
+					else:
+						current_value = None
+						new_value = None
+			except ValueError:
+				log.warn("cannot compare new value '%s' with current value '%s' by operator '%s', using '%s' directly as new value" % (val, current_value, op, new_value))
+
 		if current_value is not None:
 			self._storage_set(instance, command, current_value, device)
+		return new_value
 
 	def _execute_device_command(self, instance, command, device, new_value):
 		if command["custom"] is not None:
 			command["custom"](True, new_value, device)
 		else:
-			self._save_current_value(instance, command, device)
-			command["set"](new_value, device)
+			new_value = self._check_and_save_value(instance, command, device, new_value)
+			if new_value is not None:
+				command["set"](new_value, device)
 
 	def _execute_non_device_command(self, instance, command, new_value):
 		if command["custom"] is not None:
 			command["custom"](True, new_value)
 		else:
-			self._save_current_value(instance, command)
-			command["set"](new_value)
+			new_value = self._check_and_save_value(instance, command, None, new_value)
+			if new_value is not None:
+				command["set"](new_value)
 
 	def _cleanup_all_non_device_commands(self, instance):
 		for command in filter(lambda command: not command["per_device"], self._commands.values()):
-- 
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