CPU Frequency Scaling - Revision history

Leo: /* My CPU is stuck at a very low clock speed */

2023-01-31T18:39:36Z

My CPU is stuck at a very low clock speed

← Older revision		Revision as of 18:39, 31 January 2023
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	*Check your power supplies. A failing PSU could cause the CPU to throttle.		*Check your power supplies. A failing PSU could cause the CPU to throttle.
	*Check CPU temperature. A blocked inlet, or not enough airflow could possibly be an issue.		*Check CPU temperature. A blocked inlet, or not enough airflow could possibly be an issue.
	*Try to powercycle the server. If it uses a SMASH-CLP DRAC, try to <code>reset</code> the <code>/system1/~~pormanagement1~~</code> target (this seemed to help on a problematic server)		*Try to powercycle the server. If it uses a SMASH-CLP DRAC, try to <code>reset</code> the <code>/system1/pwrmanagement1</code> target (this seemed to help on a problematic server)

	=== My CPU clocks down under load ===		=== My CPU clocks down under load ===

Leo: /* CPU clocking down to the minimum clock speed */

2023-01-30T23:10:52Z

CPU clocking down to the minimum clock speed

← Older revision		Revision as of 23:10, 30 January 2023
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	*Check your power supplies. A failing PSU could cause the CPU to throttle.		*Check your power supplies. A failing PSU could cause the CPU to throttle.
	*Check CPU temperature. A blocked inlet, or not enough airflow could possibly be an issue.		*Check CPU temperature. A blocked inlet, or not enough airflow could possibly be an issue.
			*Try to powercycle the server. If it uses a SMASH-CLP DRAC, try to <code>reset</code> the <code>/system1/pormanagement1</code> target (this seemed to help on a problematic server)

	=== My CPU clocks down under load ===		=== My CPU clocks down under load ===

Leo: Removed Linux utils category

2022-01-01T22:27:02Z

Removed Linux utils category

← Older revision		Revision as of 22:27, 1 January 2022
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	{{Navbox Linux}}		{{Navbox Linux}}
	[[Category:Linux]]		[[Category:Linux]]
	~~[[Category:LinuxUtilities]]~~

Leo: Added categories and navbox

2021-12-30T00:47:29Z

Added categories and navbox

← Older revision		Revision as of 00:47, 30 December 2021
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	...		...
	\| lang = terminal		\| lang = terminal
	}}~~<br />~~		}}

	==See Also==		==See Also==
			*https://wiki.archlinux.org/title/CPU_frequency_scaling

	*https:~~//wiki.archlinux.org/title/CPU_frequency_scaling~~		{{Navbox Linux}}
			[[Category:Linux]]
			[[Category:LinuxUtilities]]

Leo at 22:55, 26 July 2021

2021-07-26T22:55:43Z

← Older revision		Revision as of 22:55, 26 July 2021
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	CPU clock frequency scales up and down with the CPU usage as a way to reduce power usage. On Linux, this behavior is governed by the CPU governor.		CPU clock frequency scales up and down with the CPU usage as a way to reduce power usage. On Linux, this behavior is governed by the CPU governor.

	The CPU frequency also scales down as a response to high temperature.		The CPU frequency also scales down as a response to high temperature, or if it's running certain instructions like AVX-512.

	==Linux's CPU frequency governor==		==Linux's CPU frequency governor==
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	\|}		\|}

	== Issues ==		==Issues==

	=== My CPU is stuck at a very low clock speed ===		===My CPU is stuck at a very low clock speed===
	I've had servers stuck at around 100MHz which is well below the minimum clock speed of the CPU. I wrote about it on [[Troubleshooting a Slow Linux System]] as well.		I've had servers stuck at around 100MHz which is well below the minimum clock speed of the CPU. I wrote about it on [[Troubleshooting a Slow Linux System]] as well.

	Some tips if this happens to you are:		Some tips if this happens to you are:

	* Do a BIOS update. A bug with the BIOS could make the CPU think there isn't enough power, for example.		*Do a BIOS update. A bug with the BIOS could make the CPU think there isn't enough power, for example.
	* Check your power supplies. A failing PSU could cause the CPU to throttle.		*Check your power supplies. A failing PSU could cause the CPU to throttle.
	* Check CPU temperature. A blocked inlet, or not enough airflow could possibly be an issue.		*Check CPU temperature. A blocked inlet, or not enough airflow could possibly be an issue.

	=== CPU clocking down to the minimum clock speed ===		=== My CPU clocks down under load ===
			If your CPU clocks down while under load, check if it is:

			# a thermal issue
			# a power issue
			# due to slow SIMD instructions like AVX2 or AVX-512, which will cause the core to clock down. See: https://stackoverflow.com/questions/56852812/simd-instructions-lowering-cpu-frequency/56861355#56861355

			===CPU clocking down to the minimum clock speed===
	At RCS, the servers are configured to be using the performance CPU governor in order to eek as much performance as we can from the hardware. Because of the governor setting, we expect the CPU frequency to sit somewhere between the base CPU frequency and the turbo boost frequency. However, I have observed some idle nodes at 1GHz, the minimum limit for these processors.		At RCS, the servers are configured to be using the performance CPU governor in order to eek as much performance as we can from the hardware. Because of the governor setting, we expect the CPU frequency to sit somewhere between the base CPU frequency and the turbo boost frequency. However, I have observed some idle nodes at 1GHz, the minimum limit for these processors.

Leo at 23:32, 16 July 2021

2021-07-16T23:32:33Z

@@ Line 75: / Line 75: @@
 |}
-== See Also ==
+== Issues ==
-* https://wiki.archlinux.org/title/CPU_frequency_scaling
+=== My CPU is stuck at a very low clock speed ===

Leo: /* Intel Turbo Boost frequency */

2021-07-16T23:17:53Z

Intel Turbo Boost frequency

← Older revision		Revision as of 23:17, 16 July 2021
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	\| lang = terminal		\| lang = terminal
	}}		}}
	===Types of governors===		===Types of scaling governors===
			Scaling governors are policies that affect the CPU frequency scaling algorithm.

			See: https://www.kernel.org/doc/html/v4.14/admin-guide/pm/cpufreq.html
	{\| class="wikitable"		{\| class="wikitable"
	!Governor		!Governor
	!~~Description~~		!A very brief description
			\|-
			\|performance
			\|Run the CPU at the highest frequency, as defined within the scaling_max_freq limit.
			\|-
			\|powersave
			\|Run the CPU at the lowest frequency, as defined within the scaling_min_freq limit.
	\|-		\|-
	\|ondemand		\|ondemand
	\|Dynamically ~~switch between CPU(s) available if at 95% CPU~~ load		\|Dynamically sets frequency proportional to the load of the CPUs.
	\|-
	~~\|performance~~
	~~\|Run~~ the ~~CPU at max frequency~~
	\|-		\|-
	\|conservative		\|conservative
	\|~~Dynamically switch between CPU(s) available if at 75% load~~		\|Like ondemand, but frequency changes happen in smaller steps.
	\|-
	~~\|powersave~~
	~~\|Run the CPU at the minimum~~ frequency
	\|-		\|-
	\|userspace		\|userspace
	\|Run the CPU at user specified ~~frequencies~~		\|Run the CPU at user specified frequency, controlled by writing to the <code>scaling_setspeed</code> attribute.
	\|}		\|}

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	==Some helpful commands==		==Some helpful commands==
	{\| class="wikitable"		{\| class="wikitable"
	\|+
	!Description		!Description
	!Command		!Command
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	\|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp \| sort -rn \| head -n 1 \| awk '{printf("%f", $1/1000);}'</nowiki></code>		\|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp \| sort -rn \| head -n 1 \| awk '{printf("%f", $1/1000);}'</nowiki></code>
	\|}		\|}

			== See Also ==

			* https://wiki.archlinux.org/title/CPU_frequency_scaling

Leo at 22:57, 16 July 2021

2021-07-16T22:57:12Z

← Older revision		Revision as of 22:57, 16 July 2021
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	The CPU frequency also scales down as a response to high temperature.		The CPU frequency also scales down as a response to high temperature.

	== Linux's CPU frequency governor ==		==Linux's CPU frequency governor==
	You can check your current CPU governor by running:		You can check your current CPU governor by running:
	{{Highlight		{{Highlight
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	\| lang = terminal		\| lang = terminal
	}}		}}
	On systems that do not support CPU or if for some reason Linux isn't aware of this feature, <code>cpupower</code> will return "Not Available" and the CPU pseudofiles won't be visible. On such systems, you may still see that the CPU frequency will still scale up or down depending on CPU utilization.		===Types of governors===

	=== Types of governors ===
	{\| class="wikitable"		{\| class="wikitable"
	!Governor		!Governor
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	\|}		\|}

	==~~= CPU boost~~ frequency ===		==Intel Turbo Boost frequency==
	Some CPUs support a boost frequency~~. A~~ CPU ~~clocked at 2.5GHz~~ can ~~boost to 3.2GHz if~~ power and thermal ~~requirements are met~~. ~~This~~ frequency ~~may drop as~~ the CPU ~~heats up~~.		Some Intel CPUs support a turbo boost frequency where a CPU can clock faster than its stock speed depending on available power and thermal conditions. Refer to the CPU's specification to determine a particular CPU's turbo boost frequency.

			I have observed on some compute servers that the CPU will run somewhere between the base frequency and the turbo boost frequency when the temperature is around the mid 70's Celsius when under full load. I'm not sure why this is the case.

	=== Some helpful commands ===		==Some helpful commands==
	{\| class="wikitable"		{\| class="wikitable"
	\|+		\|+
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	\|-		\|-
	\|Get average CPU core frequency		\|Get average CPU core frequency
	\|<code><nowiki>grep MHz /proc/cpuinfo \| awk '{print $4}' \| awk '{temp+=$1;n++} END{printf("%f", temp/n);}'</nowiki></code>		\|<code><nowiki>grep MHz /proc/cpuinfo \| awk '{print $4}' \| awk '{temp+=$1;n++} END{printf("%f", temp/n);}'</nowiki></code>
	\|-		\|-
	\|Get max CPU core frequency		\|Get max CPU core frequency
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	\|-		\|-
	\|Get average CPU temperature		\|Get average CPU temperature
	\|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp \| awk '{temp+=$1;n++} END{printf("%f", temp/n/1000);}'</nowiki></code>		\|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp \| awk '{temp+=$1;n++} END{printf("%f", temp/n/1000);}'</nowiki></code>
	\|-		\|-
	\|Get max CPU temperature		\|Get max CPU temperature
	\|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp \| sort -rn \| head -n 1 \| awk '{printf("%f", ~~temp/n~~/1000);}'</nowiki></code>		\|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp \| sort -rn \| head -n 1 \| awk '{printf("%f", $1/1000);}'</nowiki></code>
	\|}		\|}

Leo: Created page with "CPU clock frequency scales up and down with the CPU usage as a way to reduce power usage. On Linux, this behavior is governed by the CPU governor. The CPU frequency also sc..."

2021-07-16T22:20:52Z

Created page with "CPU clock frequency scales up and down with the CPU usage as a way to reduce power usage. On Linux, this behavior is governed by the CPU governor. The CPU frequency also sc..."

New page

CPU clock frequency scales up and down with the CPU usage as a way to reduce power usage. On Linux, this behavior is governed by the CPU governor.

The CPU frequency also scales down as a response to high temperature.

== Linux's CPU frequency governor ==
You can check your current CPU governor by running:
{{Highlight
| code = # cpupower frequency-info --governors
analyzing CPU 0:
available cpufreq governors: performance powersave
| lang = terminal
}}
Alternatively, you may check <code>/sys/devices/system/cpu</code> and see the setting for each CPU core.
{{Highlight
| code = # cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
performance
performance
performance
performance
performance
performance
| lang = terminal
}}
On systems that do not support CPU or if for some reason Linux isn't aware of this feature, <code>cpupower</code> will return "Not Available" and the CPU pseudofiles won't be visible. On such systems, you may still see that the CPU frequency will still scale up or down depending on CPU utilization.

=== Types of governors ===
{| class="wikitable"
!Governor
!Description
|-
|ondemand
|Dynamically switch between CPU(s) available if at 95% CPU load
|-
|performance
|Run the CPU at max frequency
|-
|conservative
|Dynamically switch between CPU(s) available if at 75% load
|-
|powersave
|Run the CPU at the minimum frequency
|-
|userspace
|Run the CPU at user specified frequencies
|}

=== CPU boost frequency ===
Some CPUs support a boost frequency. A CPU clocked at 2.5GHz can boost to 3.2GHz if power and thermal requirements are met. This frequency may drop as the CPU heats up.

=== Some helpful commands ===
{| class="wikitable"
|+
!Description
!Command
|-
|Get all CPU core frequencies
|<code>grep MHz /proc/cpuinfo</code>
|-
|Get average CPU core frequency
|<code><nowiki>grep MHz /proc/cpuinfo | awk '{print $4}' | awk '{temp+=$1;n++} END{printf("%f", temp/n);}'</nowiki></code>
|-
|Get max CPU core frequency
|<code><nowiki>grep MHz /proc/cpuinfo | awk '{print $4}' | sort -rn | head -n 1</nowiki></code>
|-
|Get min CPU core frequency
|<code><nowiki>grep MHz /proc/cpuinfo | awk '{print $4}' | sort -n | head -n 1</nowiki></code>
|-
|Get average CPU temperature
|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp | awk '{temp+=$1;n++} END{printf("%f", temp/n/1000);}'</nowiki></code>
|-
|Get max CPU temperature
|<code><nowiki>cat /sys/class/thermal/thermal_zone*/temp | sort -rn | head -n 1 | awk '{printf("%f", temp/n/1000);}'</nowiki></code>
|}