{{tag>Brouillon CPU Matériel Kernel Linux}}

= Gérer les CPUs sous GNU/Linux

Voir 
* [[temperature_materiel_cpu_carte_mere_debian_lm-sensors|Température CPU]]
* [[https://www.grid5000.fr/w/CPU_parameters]]
* https://www.deltasight.fr/processeurs-gestion-energie-frequence/


== Notes

Outils :
  * lscpu
  * chcpu
  * cpufreq-info
  * CoreCtrl
  * turbostat
  * cpupower
  * powertop
  * rdmsr / wrmsr (msr-tools)
  * kvm-ok / check-bios-nx (cpu-checker)

Notions :
  * Systèmes multi-processeurs (NUMA SMP)
  * Systèmes multi-cœurs (SMP) 
  * Systèmes multi-threads (SMT)


Params Kernel :
* nr_cpus



== Infos nombre de cores threads CPU

Nombre de threads
<code bash>
grep ^processor /proc/cpuinfo
</code>

Nous avons une valeurs par thread.
C'est donc la derniere valeur +1 qui donne le nombre de threads (si un seul CPU physique)

Nombre de cores
<code bash>
grep '^cpu cores' /proc/cpuinfo
</code>

Toutes les valeurs sont identiques si un seul CPU physique




== CPUFrequtils

Voir aussi : [[https://doc.ubuntu-fr.org/intel_p-state|intel_p-state]]

Gérer la fréquence cpu

<code bash>
service cpufrequtils stop
</code>

<code bash>
#!/bin/sh -e
#
# rc.local
echo "conservative" >/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo "conservative" >/sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
echo "conservative" >/sys/devices/system/cpu/cpu2/cpufreq/scaling_governor
#echo "conservative" >/sys/devices/system/cpu/cpu3/cpufreq/scaling_governor
# echo "performance" >  /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
exit 0
</code>

Fichier à exécuter en root pour changer le gouverneur. Choix possible selon la configuration du noyau : conservative, ondemand, powersave, performance.

    Avec cpufrequtils : (en root)

<code bash>
cp /usr/share/doc/cpufrequtils/examples/cpufrequtils.sample /etc/default/cpufrequtils

cpufreq-set -c 0 -d 2100000 -u 3300000

service cpufrequtils reload
</code>
    -c : numéro processeur
    -d : freq min
    -u : freq max
    -f : freq exact voulu


== Notes cpufreq

Voir : 
* https://www.kernel.org/doc/html/v4.14/admin-guide/pm/cpufreq.html
* https://www.kernel.org/doc/Documentation/cpu-freq/user-guide.txt
* https://doc.ubuntu-fr.org/cpu-frequtils
* https://wiki.debian.org/HowTo/CpuFrequencyScaling
* https://wiki.archlinux.org/index.php/CPU_frequency_scaling
* https://www.linuxquestions.org/questions/slackware-14/locking-all-cpu%27s-to-their-maximum-frequency-4175607506/
* https://www.thomas-krenn.com/en/wiki/Disable_CPU_Power_Saving_Management_in_BIOS
* https://bbs.archlinux.org/viewtopic.php?id=163253
* https://doc.ubuntu-fr.org/intel_p-state

<code bash>
grep MHz /proc/cpuinfo
</code>


<code bash>
apt-get install linux-cpupower
cpupower
</code>

<code ->
$ cpupower frequency-info -g
analyzing CPU 0:
  available cpufreq governors: Not Available

$ cpupower frequency-info
analyzing CPU 0:
  no or unknown cpufreq driver is active on this CPU
  CPUs which run at the same hardware frequency: Not Available
  CPUs which need to have their frequency coordinated by software: Not Available
  maximum transition latency:  Cannot determine or is not supported.
  hardware limits: Not Available
  available cpufreq governors: Not Available
  Unable to determine current Policy
  current CPU frequency: Unable to call hardware
  current CPU frequency:  Unable to call to kernel
  boost state support:
    Supported: yes
    Active: yes
</code>


If you have Turbo Boost enabled in the UEFI/BIOS, you can turn boost on (1) or off (0) by running
<code bash>
echo 1 > /sys/devices/system/cpu/cpufreq/boost
</code>

Limite d'utilisation du CPU en %
<code ->
# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct 
100
</code>

<code bash>
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
</code>

Exemble de "gorvernors" possible
* performance
* powersave
* userspace
* ondemand
* conservative

<code bash>
cpufreq-set -r -u 2.24Ghz
#cpufreq-set --cpu 0 --governor conservative
cpufreq-set -r -g performance

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors 
echo "performance" |tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor 

#echo "3900000" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
</code>

''/etc/default/grub''
<code bash>
CMDLINE_LINUX_DEFAULT="quiet splash intel_pstate=disable processor.ignore_ppc=1"
</code>

<code bash>
update-grub
</code>

Pour remplacer ''intel_pstate'' par ''acpi-cpufreq''
<code bash>
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_driver
</code>

La liste des drivers ici :
<code bash>
ls -1 /lib/modules/`uname -r`/kernel/drivers/cpufreq/
</code>


== BIOS frequency limitation

Source : https://wiki.archlinux.org/index.php/CPU_frequency_scaling

<code bash>
cat /sys/devices/system/cpu/cpu0/cpufreq/bios_limit
</code>


For trying this temporarily change the value in /sys/module/processor/parameters/ignore_ppc from 0 to 1. 

<code bash>
echo 1 > /sys/module/processor/parameters/ignore_ppc
</code>

For setting it permanent refer to Kernel modules or just read on. Add processor.ignore_ppc=1 to your kernel boot line or create

''/etc/modprobe.d/ignore_ppc.conf''
<code bash>

# If the frequency of your machine gets wrongly limited by BIOS, this should help
options processor ignore_ppc=1
</code>

----
Avec cpulimit

<code bash>
sudo apt-get install cpulimit
</code>

http://www.linuxscrew.com/2012/07/03/limit-cpu-usage-of-linux-process/


== Perf 


perf

<code bash>
apt-get install linux-base linux-tools
</code>

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4b715d24f4f14731c7b553cbb8604fe865cb8d3c

Voir :
* https://developers.redhat.com/articles/2023/09/29/how-we-solved-hotspot-performance-puzzle

<code bash>
# Disable SMP
echo off > /sys/devices/system/cpu/smt/control

# Disable THP
echo "never" > /sys/kernel/mm/transparent_hugepage/enabled

# Disable turbo boost
echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo
</code>


=== commande perf

Voir :
  * https://developers.redhat.com/articles/2023/07/31/frame-pointers-untangling-unwinding?sc_cid=7013a000003Sm66AAC
  * https://www.brendangregg.com/perf.html
  * https://elinux.org/images/d/d0/Moll--cycle_accurate_profiling_with_perf.pdf


== Nombre de core / CPU

/usr/bin/nproc (coreutils)

getconf _NPROCESSORS_ONLN

== Notes

service cpufrequtils stop

echo "performance" >  /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

noatime

Swap config

Blacklist module

== irqbalance
/proc/interrupts
cat /proc/irq/3/smp_affinity

cpupower

== Hotplug 

http://www.linux-kvm.org/page/CPUHotPlug

* switch to the monitor
* type ''cpu_set <n+1> online''
* A new cpu should appear on /sys/devices/system/cpu
* bring it online by writting 1 to the "online" file inside that directory on guest
* Try adding as many cpus as possible, and make sure we at least do not crash.

==  Monitoring

pcp
http://www.pcp.io/docs/guide.html
https://www.youtube.com/watch?v=zrAjevr8_Ds

== Kernel

Real-time kernel ?

http://www.tldp.org/LDP/solrhe/Securing-Optimizing-Linux-RH-Edition-v1.3/chap7sec80.html

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/pdf/Performance_Tuning_Guide/Red_Hat_Enterprise_Linux-6-Performance_Tuning_Guide-en-US.pdf

https://wiki.archlinux.org/index.php/maximizing_performance

https://tweaked.io/guide/kernel/

http://www.redhat.com/promo/summit/2008/downloads/pdf/Wednesday_1015am_John_Shakshober_and_Larry_Woodman_Decoding_the_Code.pdf

http://www.brendangregg.com/blog/2015-03-03/performance-tuning-linux-instances-on-ec2.html

https://oracle-base.com/articles/linux/configuring-huge-pages-for-oracle-on-linux-64


== Autres

<code ->
root# dmidecode|grep HTT
HTT (Hyper-Threading Technology)
HTT (Hyper-Threading Technology)

root# egrep 'siblings|cpu cores' /proc/cpuinfo | head -2
siblings : 2
cpu cores : 1

root# grep '^flags\b' /proc/cpuinfo | tail -1
flags : fpu de tsc msr pae mce cx8 apic sep mca cmov pat clflush acpi mmx
fxsr sse sse2 ss ht syscall nx lm constant_tsc rep_good nopl nonstop_tsc pni
pclmulqdq est ssse3 cx16 sse4_1 sse4_2 popcnt aes f16c rdrand hypervisor lahf_lm ida
arat epb pln pts dts fsgsbase erms

root# dmidecode |grep Count # tests that HTT is available *and* enabled
Core Count: 1
Thread Count: 2
Core Count: 1
Thread Count: 2
</code>
Source : https://www.oracle.com/docs/tech/ovm-performance.pdf