Linux Dynamic Frequency Scaling - Revision history

JulienB: /* Links */

2017-10-03T08:52:12Z

Links

← Older revision		Revision as of 10:52, 3 October 2017
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	==Links==		==Links==
			* https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/Documentation/cpu-freq/governors.txt?h=v4.9.52
	* http://lxr.linux.no/linux+v2.6.37/Documentation/cpu-freq/user-guide.txt		* http://lxr.linux.no/linux+v2.6.37/Documentation/cpu-freq/user-guide.txt

	[[Category:Power Management]]		[[Category:Power Management]]

JulienB: /* Usage (sysfs) */

2017-10-03T08:50:03Z

Usage (sysfs)

← Older revision		Revision as of 10:50, 3 October 2017
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	<pre class="apf">		<pre class="apf">
	# cat scaling_available_governors		# cat scaling_available_governors
	conservative ondemand userspace powersave performance		conservative ondemand userspace powersave interactive performance
	</pre>		</pre>
	* change governor:		* change governor:

JulienB: /* Linux configuration */

2017-10-03T08:48:54Z

Linux configuration

← Older revision		Revision as of 10:48, 3 October 2017
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	</pre>		</pre>

	frequency scaling handling is done in ''arch/arm/plat-mxc/cpufreq.c'' or ''arch/arm/mach-mx2/cpufreq_imx27.c''		In old Linux kernels (before device tree), frequency scaling handling is done in ''arch/arm/plat-mxc/cpufreq.c'' or ''arch/arm/mach-mx2/cpufreq_imx27.c''

	==To know whether the driver is working==		==To know whether the driver is working==

JulienB at 17:58, 28 December 2016

2016-12-28T17:58:38Z

← Older revision		Revision as of 19:58, 28 December 2016
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	==Introduction==		==Introduction==
	Dynamic Frequency Scaling aka DFS is available on [[APF27]], [[APF51]], [[APF28]] and [[~~APF6~~]] based systems. It allows you to control CPU speed according to module activity.		Dynamic Frequency Scaling aka DFS is available on [[APF27]], [[APF51]], [[APF28]], [[APF6]] and [[OPOS6UL]] based systems. It allows you to control CPU speed according to module activity.

	==Linux configuration==		==Linux configuration==
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	{\| border="1" cellpadding="10" cellspacing="0" summary="DFS check depending on kernel version" class="wikitable"		{\| border="1" cellpadding="10" cellspacing="0" summary="DFS check depending on kernel version" class="wikitable"
	\|- style="background:#efefef;" align="center"		\|- style="background:#efefef;" align="center"
	! APF27 / APF28 / APF51 \|\| APF6		! APF27 / APF28 / APF51 \|\| APF6 / OPOS6UL
	\|---		\|---
	\|<pre class="apf">		\|<pre class="apf">

JulienB at 14:21, 18 March 2015

2015-03-18T14:21:12Z

← Older revision		Revision as of 16:21, 18 March 2015
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	~~{{Under_Construction}}~~

	==Introduction==		==Introduction==
	Dynamic Frequency Scaling aka DFS is available on [[APF27]], [[APF51]], [[APF28]] and [[APF6]] based systems.		Dynamic Frequency Scaling aka DFS is available on [[APF27]], [[APF51]], [[APF28]] and [[APF6]] based systems. It allows you to control CPU speed according to module activity.

			==Linux configuration==
	You need to have a kernel with the CPUfreq drivers built-in (done by default when available):		You need to have a kernel with the CPUfreq drivers built-in (done by default when available):
	<pre class="host">		<pre class="host">
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	</pre>		</pre>

	~~==Linux configuration==~~
	<pre class="config">		<pre class="config">
	CPU Power Management --->		CPU Power Management --->

JulienB: /* Usage (sysfs) */

2015-03-18T14:19:30Z

Usage (sysfs)

← Older revision		Revision as of 16:19, 18 March 2015
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	# ls		# ls
	</pre>		</pre>
			{{Note\|[[APF6]] may have up to 4 CPU cores so you may end up with ''cpu0'', ''cpu1'', ''cpu2'', ''cpu3'' in ''/sys/devices/system/cpu/''}}
	* identify the current governor:		* identify the current governor:
	<pre class="apf">		<pre class="apf">

JulienB: /* Effect on current consumption */

2015-03-18T14:17:41Z

Effect on current consumption

← Older revision		Revision as of 16:17, 18 March 2015
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	This is caused by the "doze mode" : when all processes are sleeping, the kernel turns off the CPU clock until the next IO or timer event.		This is caused by the "doze mode" : when all processes are sleeping, the kernel turns off the CPU clock until the next IO or timer event.

	When there is a 100% CPU activity, the effect of the CPU frequency can be observed with a ~~ammeter~~.		When there is a 100% CPU activity, the effect of the CPU frequency can be observed with a ampmeter.

	The % CPU activity per process can be checked with the '''top''' command, which is supported by Busybox (but it may be necessary to configure and rebuild busybox to have it)		The % CPU activity per process can be checked with the '''top''' command, which is supported by Busybox (but it may be necessary to configure and rebuild busybox to have it)
	{{Note\| If you make current measurements using a development board like APF27dev or APF51dev, take care of making all the measurement with the '''same supply voltage'''.		{{Note\| If you make current measurements using a development board like [[APF27dev]] or [[APF51dev]], take care of making all the measurement with the '''same supply voltage'''.
	Unlike linear regulators, the switching regulator of the board reduces the current consumed when the input voltage is increased (to keep the power constant)}}		Unlike linear regulators, the switching regulator of the board reduces the current consumed when the input voltage is increased (to keep the power constant)}}

JulienB: /* Usage (sysfs) */

2015-03-18T14:15:38Z

Usage (sysfs)

← Older revision		Revision as of 16:15, 18 March 2015
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	<pre class="apf">		<pre class="apf">
	# echo powersave > scaling_governor		# echo powersave > scaling_governor
	~~</pre>~~
	* change frequency manually (here 133MHz). '''Requires userspace governor !''' :
	~~<pre class="apf">~~
	~~# echo 133000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed~~
	</pre>		</pre>
	* To know current CPU frequency (here 160MHz):		* To know current CPU frequency (here 160MHz):
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	800000 585		800000 585
	</pre>		</pre>
			* change frequency manually (here 133MHz). '''Requires userspace governor !''' :
			<pre class="apf">
			# echo 133000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
			</pre>

	==Effect on current consumption==		==Effect on current consumption==
	When there is little activity, the CPU frequency has nearly no visible effect on the current consumed.		When there is little activity, the CPU frequency has nearly no visible effect on the current consumed.

JulienB: /* Introduction */

2015-03-18T14:14:46Z

Introduction

← Older revision		Revision as of 16:14, 18 March 2015
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	==Introduction==		==Introduction==
	Dynamic Frequency Scaling aka DFS is ~~only~~ available on [[APF27]] and [[~~APF51~~]] based systems.		Dynamic Frequency Scaling aka DFS is available on [[APF27]], [[APF51]], [[APF28]] and [[APF6]] based systems.

	You need to ~~make~~ a kernel with the CPUfreq drivers built ~~inside~~ :		You need to have a kernel with the CPUfreq drivers built-in (done by default when available):
	<pre class="host">		<pre class="host">
	$ make linux-menuconfig		$ make linux-menuconfig

JulienB: /* To know whether the driver is working */

2015-03-18T14:12:47Z

To know whether the driver is working

← Older revision		Revision as of 16:12, 18 March 2015
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	==To know whether the driver is working==		==To know whether the driver is working==
	<pre class="apf">		{\| border="1" cellpadding="10" cellspacing="0" summary="DFS check depending on kernel version" class="wikitable"
			\|- style="background:#efefef;" align="center"
			! APF27 / APF28 / APF51 \|\| APF6
			\|---
			\|<pre class="apf">
	# dmesg \| grep freq		# dmesg \| grep freq
	i.MXC CPU frequency driver		i.MXC CPU frequency driver
	</pre>		</pre>
			\|Should be activated/working by default :-)
			\|}

	==Usage (sysfs)==		==Usage (sysfs)==