Merge pull request #622 from zacikpa/reduce-ipi

Avoid unnecessary inter-processor interrupts by checking that writes are necessary

tuned/plugins/plugin_cpu.py

@@ -196,7 +196,8 @@ def __init__(self, *args, **kwargs):
 		self._is_x86 = False
 		self._is_intel = False
 		self._is_amd = False
-		self._has_energy_perf_bias = False
+		self._has_hwp_epp = False
+		self._has_energy_perf_policy_and_bias = False
 		self._has_intel_pstate = False
 		self._has_amd_pstate = False
 		self._has_pm_qos_resume_latency_us = None
@@ -259,25 +260,29 @@ def _check_arch(self):
 		else:
 			log.info("We are running on %s (non x86)" % self._arch)
 
+		self._has_hwp_epp = consts.CFG_CPU_EPP_FLAG in self._get_cpuinfo_flags()
+
 		if self._is_intel:
-			# Check for x86_energy_perf_policy, ignore if not available / supported
-			self._check_energy_perf_bias()
+			# When hwp_epp is not supported, we check for EPB via x86_energy_perf_policy.
+			# When it is supported, EPB should be accessible via sysfs.
+			if not self._has_hwp_epp:
+				self._check_energy_perf_policy_and_bias()
 			# Check for intel_pstate
 			self._check_intel_pstate()
 
 		if self._is_amd:
 			# Check for amd-pstate
 			self._check_amd_pstate()
 
-	def _check_energy_perf_bias(self):
-		self._has_energy_perf_bias = False
+	def _check_energy_perf_policy_and_bias(self):
+		"""Check for EPB via x86_energy_perf_policy, warn if the tool is not available or EPB unsupported."""
 		retcode_unsupported = 1
 		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
+			self._has_energy_perf_policy_and_bias = True
 		elif retcode < 0:
 			log.warning("unable to run x86_energy_perf_policy tool, ignoring CPU energy performance bias, is the tool installed?")
 		else:
@@ -359,7 +364,7 @@ def _get_intel_pstate_attr(self, attr):
 
 	def _set_intel_pstate_attr(self, attr, val):
 		if val is not None:
-			self._cmd.write_to_file("/sys/devices/system/cpu/intel_pstate/%s" % attr, val)
+			self._cmd.write_to_file("/sys/devices/system/cpu/intel_pstate/%s" % attr, val, ignore_same=True)
 
 	def _getset_intel_pstate_attr(self, attr, value):
 		if value is None:
@@ -524,7 +529,7 @@ def _set_governor(self, governors, device, sim, remove):
 					log.info("setting governor '%s' on cpu '%s'"
 							% (governor, device))
 					self._cmd.write_to_file("/sys/devices/system/cpu/%s/cpufreq/scaling_governor"
-							% device, governor, no_error = [errno.ENOENT] if remove else False)
+							% device, governor, no_error = [errno.ENOENT] if remove else False, ignore_same=True)
 				break
 			elif not sim:
 				log.debug("Ignoring governor '%s' on cpu '%s', it is not supported"
@@ -614,14 +619,14 @@ def _set_energy_perf_bias(self, energy_perf_bias, device, sim, remove):
 
 		# It should be writen straight to sysfs energy_perf_bias file if requested on newer processors
 		# see rhbz#2095829
-		if consts.CFG_CPU_EPP_FLAG in self._get_cpuinfo_flags():
+		if self._has_hwp_epp:
 			energy_perf_bias_path = self._energy_perf_bias_path(cpu_id)
 			if os.path.exists(energy_perf_bias_path):
 				if not sim:
 					for val in vals:
 						val = val.strip()
 						if self._cmd.write_to_file(energy_perf_bias_path, val, \
-							no_error = [errno.ENOENT] if remove else False):
+							no_error = [errno.ENOENT] if remove else False, ignore_same=True):
 								log.info("energy_perf_bias successfully set to '%s' on cpu '%s'"
 										 % (val, device))
 								break
@@ -634,7 +639,7 @@ def _set_energy_perf_bias(self, energy_perf_bias, device, sim, remove):
 				log.error("Failed to set energy_perf_bias on cpu '%s' because energy_perf_bias file does not exist."
 						  % device)
 				return None
-		elif self._has_energy_perf_bias:
+		elif self._has_energy_perf_policy_and_bias:
 			if not sim:
 				for val in vals:
 					val = val.strip()
@@ -690,11 +695,11 @@ def _get_energy_perf_bias(self, device, ignore_missing=False):
 			log.debug("%s is not online, skipping" % device)
 			return None
 		cpu_id = device.lstrip("cpu")
-		if consts.CFG_CPU_EPP_FLAG in self._get_cpuinfo_flags():
+		if self._has_hwp_epp:
 			energy_perf_bias_path = self._energy_perf_bias_path(cpu_id)
 			if os.path.exists(energy_perf_bias_path):
 				energy_perf_bias = self._energy_perf_policy_to_human_v2(self._cmd.read_file(energy_perf_bias_path))
-		elif self._has_energy_perf_bias:
+		elif self._has_energy_perf_policy_and_bias:
 			retcode, lines = self._cmd.execute(["x86_energy_perf_policy", "-c", cpu_id, "-r"])
 			if retcode == 0:
 				for line in lines.splitlines():
@@ -756,7 +761,7 @@ def _set_energy_performance_preference(self, energy_performance_preference, devi
 				for val in vals:
 					if val in avail_vals:
 						self._cmd.write_to_file(self._pstate_preference_path(cpu_id), val, \
-							no_error = [errno.ENOENT] if remove else False)
+							no_error = [errno.ENOENT] if remove else False, ignore_same=True)
 						log.info("Setting energy_performance_preference value '%s' for cpu '%s'" % (val, device))
 						break
 					else:

tuned/plugins/plugin_sysctl.py

@@ -166,45 +166,18 @@ def _get_sysctl_path(self, option):
 
 	def _read_sysctl(self, option):
 		path = self._get_sysctl_path(option)
-		try:
-			with open(path, "r") as f:
-				line = ""
-				for i, line in enumerate(f):
-					if i > 0:
-						log.error("Failed to read sysctl parameter '%s', multi-line values are unsupported"
-								% option)
-						return None
-				value = line.strip()
-			log.debug("Value of sysctl parameter '%s' is '%s'"
-					% (option, value))
-			return value
-		except (OSError, IOError) as e:
-			if e.errno == errno.ENOENT:
-				log.error("Failed to read sysctl parameter '%s', the parameter does not exist"
-						% option)
-			else:
-				log.error("Failed to read sysctl parameter '%s': %s"
-						% (option, str(e)))
+		content = self._cmd.read_file(path, err_ret=None)
+		if content is None:
 			return None
+		content = content.strip()
+		if len(content.split("\n")) > 1:
+			log.error("Failed to read sysctl parameter '%s', multi-line values are unsupported" % option)
+			return None
+		return content
 
 	def _write_sysctl(self, option, value, ignore_missing = False):
 		path = self._get_sysctl_path(option)
 		if os.path.basename(path) in DEPRECATED_SYSCTL_OPTIONS:
-			log.error("Refusing to set deprecated sysctl option %s"
-					% option)
-			return False
-		try:
-			log.debug("Setting sysctl parameter '%s' to '%s'"
-					% (option, value))
-			with open(path, "w") as f:
-				f.write(value)
-			return True
-		except (OSError, IOError) as e:
-			if e.errno == errno.ENOENT:
-				log_func = log.debug if ignore_missing else log.error
-				log_func("Failed to set sysctl parameter '%s' to '%s', the parameter does not exist"
-						% (option, value))
-			else:
-				log.error("Failed to set sysctl parameter '%s' to '%s': %s"
-						% (option, value, str(e)))
+			log.error("Refusing to set deprecated sysctl option %s" % option)
 			return False
+		return self._cmd.write_to_file(path, value, no_error=[errno.ENOENT] if ignore_missing else False, ignore_same=True)

tuned/plugins/plugin_sysfs.py

@@ -87,4 +87,4 @@ def _read_sysfs(self, sysfs_file):
 			return None
 
 	def _write_sysfs(self, sysfs_file, value):
-		return self._cmd.write_to_file(sysfs_file, value)
+		return self._cmd.write_to_file(sysfs_file, value, ignore_same=True)

tuned/utils/commands.py

@@ -90,14 +90,15 @@ def re_lookup(self, d, s, r = None):
 			return list(d.values())[mo.lastindex - 1]
 		return None
 
-	def write_to_file(self, f, data, makedir = False, no_error = False):
+	def write_to_file(self, f, data, makedir = False, no_error = False, ignore_same = False):
 		"""Write data to a file.
 
 		Parameters:
 		f -- filename where to write
 		data -- data to write
 		makedir -- if True and the path doesn't exist, it will be created
 		no_error -- if True errors are silenced, it can be also list of ignored errnos
+		ignore_same -- if True and the write would not change the file, it is skipped
 
 		Return:
 		bool -- True on success
@@ -110,6 +111,9 @@ def write_to_file(self, f, data, makedir = False, no_error = False):
 		try:
 			if makedir:
 				os.makedirs(d)
+			if ignore_same and self.read_file(f, no_error=True).strip() == str(data):
+				self._debug("Skipping the write to file '%s', the content would not change" % f)
+				return True
 			fd = open(f, "w")
 			fd.write(str(data))
 			fd.close()
@@ -124,9 +128,9 @@ def write_to_file(self, f, data, makedir = False, no_error = False):
 	def read_file(self, f, err_ret = "", no_error = False):
 		old_value = err_ret
 		try:
-			f = open(f, "r")
-			old_value = f.read()
-			f.close()
+			fd = open(f, "r")
+			old_value = fd.read()
+			fd.close()
 		except (OSError,IOError) as e:
 			if not no_error:
 				self._error("Error when reading file '%s': '%s'" % (f, e))