Disk plugin: make hdparm device checks lazy

The disk plugin checks each device for hdparm
support during initialization. When using many disk
devices, this can lead to unwanted delays in profile
application.

This change makes the hdparm check lazy by postponing
it to the moment when hdparm is actually needed, i.e.,
during dynamic tuning or when setting spindown/apm.
Each device is checked at most once - the plugin now stores
the sets of hdparm-supported devices and hdparm-unsupported
devices).

Resolves: RHEL-6891

tuned/plugins/plugin_disk.py

@@ -100,19 +100,20 @@ def _init_devices(self):
 		self._devices_supported = True
 		self._use_hdparm = True
 		self._free_devices = set()
-		self._hdparm_apm_devices = set()
+		self._hdparm_apm_device_support = dict()
 		for device in self._hardware_inventory.get_devices("block"):
 			if self._device_is_supported(device):
 				self._free_devices.add(device.sys_name)
-				if self._use_hdparm and self._is_hdparm_apm_supported(device.sys_name):
-					self._hdparm_apm_devices.add(device.sys_name)
-
 		self._assigned_devices = set()
 
 	def _get_device_objects(self, devices):
 		return [self._hardware_inventory.get_device("block", x) for x in devices]
 
 	def _is_hdparm_apm_supported(self, device):
+		if not self._use_hdparm:
+			return False
+		if device in self._hdparm_apm_device_support:
+			return self._hdparm_apm_device_support[device]
 		(rc, out, err_msg) = self._cmd.execute(["hdparm", "-C", "/dev/%s" % device], \
 				no_errors = [errno.ENOENT], return_err=True)
 		if rc == -errno.ENOENT:
@@ -122,10 +123,13 @@ def _is_hdparm_apm_supported(self, device):
 		elif rc:
 			log.info("Device '%s' not supported by hdparm" % device)
 			log.debug("(rc: %s, msg: '%s')" % (rc, err_msg))
+			self._hdparm_apm_device_support[device] = False
 			return False
 		elif "unknown" in out:
 			log.info("Driver for device '%s' does not support apm command" % device)
+			self._hdparm_apm_device_support[device] = False
 			return False
+		self._hdparm_apm_device_support[device] = True
 		return True
 
 	@classmethod
@@ -232,7 +236,7 @@ def _drive_spinning(self, device):
 		return not "standby" in out and not "sleeping" in out
 
 	def _instance_update_dynamic(self, instance, device):
-		if not device in self._hdparm_apm_devices:
+		if not self._is_hdparm_apm_supported(device):
 			return
 		load = instance._load_monitor.get_device_load(device)
 		if load is None:
@@ -315,7 +319,7 @@ def _instance_apply_dynamic(self, instance, device):
 		# At the moment we support dynamic tuning just for devices compatible with hdparm apm commands
 		# If in future will be added new functionality not connected to this command,
 		# it is needed to change it here
-		if device not in self._hdparm_apm_devices:
+		if not self._is_hdparm_apm_supported(device):
 			log.info("There is no dynamic tuning available for device '%s' at time" % device)
 		else:
 			super(DiskPlugin, self)._instance_apply_dynamic(instance, device)
@@ -350,7 +354,7 @@ def _get_elevator(self, device, ignore_missing=False):
 
 	@command_set("apm", per_device=True)
 	def _set_apm(self, value, device, sim, remove):
-		if device not in self._hdparm_apm_devices:
+		if not self._is_hdparm_apm_supported(device):
 			if not sim:
 				log.info("apm option is not supported for device '%s'" % device)
 				return None
@@ -366,7 +370,7 @@ def _set_apm(self, value, device, sim, remove):
 
 	@command_get("apm")
 	def _get_apm(self, device, ignore_missing=False):
-		if device not in self._hdparm_apm_devices:
+		if not self._is_hdparm_apm_supported(device):
 			if not ignore_missing:
 				log.info("apm option is not supported for device '%s'" % device)
 			return None
@@ -390,7 +394,7 @@ def _get_apm(self, device, ignore_missing=False):
 
 	@command_set("spindown", per_device=True)
 	def _set_spindown(self, value, device, sim, remove):
-		if device not in self._hdparm_apm_devices:
+		if not self._is_hdparm_apm_supported(device):
 			if not sim:
 				log.info("spindown option is not supported for device '%s'" % device)
 				return None
@@ -406,7 +410,7 @@ def _set_spindown(self, value, device, sim, remove):
 
 	@command_get("spindown")
 	def _get_spindown(self, device, ignore_missing=False):
-		if device not in self._hdparm_apm_devices:
+		if not self._is_hdparm_apm_supported(device):
 			if not ignore_missing:
 				log.info("spindown option is not supported for device '%s'" % device)
 			return None