fabic974 random (binary) wanderings in the philament empires…

Linux CPU frequency troobleshooting

Sequel of yesterday’s post about compiling LLVM Clang: it hadn’t completed this morning due to my laptop’s CPU “governor” thing being “powersave”.

The morning after – Sept. 15th – 50% done only ?! o_o`

It shall have completed a long while ago – 15 min. load avg. is 3.6 – compilation is still goin’ on with 3 jobs using >80% of CPUs – what the heck ? – damn laptop must have gone in low-power consumption mode somehow – I do remember having closed the lid of it inadvertently before dozzing off: it went in sleep mode, I woke it up and stuff continued ; but probably did that trigger some sort of CPU powersave state.

Monitoring CPU frequency :

Shows that it hardly ever gets above 1GHz frequency :

[fabi@wall] ~/dev/llvm/build (master ✗)  watch -d -n1 \
    grep -E "'^(processor|cpu MHz|model name|$)'" /proc/cpuinfo

processor	: 0
model name	: Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu MHz		: 427.781

processor	: 1
model name	: Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu MHz		: 411.750

processor	: 2
model name	: Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu MHz		: 427.675

processor	: 3
model name	: Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu MHz		: 410.800

Performance troobleshooting :

Did try to unplug-plug the power cable, didn’t do it ;

Did try to start laptop-mode daemon too, didn’t do it – stopped it as it tends to spin down the hard-drive too often ;

Reading archlinux’s CPU frequency scaling, and investigating how to trigger usage of a performance CPU frequency governor :

[root@wall] lib # find /proc /sys -name \*pstate\*

Seems not to be under /sys/devices/system/cpu/intel_pstate/ :

[root@wall] lib # grep ^ /sys/devices/system/cpu/intel_pstate/* | column -t -s:
/sys/devices/system/cpu/intel_pstate/max_perf_pct  100
/sys/devices/system/cpu/intel_pstate/min_perf_pct  25
/sys/devices/system/cpu/intel_pstate/no_turbo      0

[root@wall] lib # uname -a
Linux sabayon 3.12.0-sabayon #1 SMP Mon Sep 1 02:30:34 UTC 2014 x86_64 Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz GenuineIntel GNU/Linux

[root@wall] lib # ls /lib/modules/$(uname -r)/kernel/drivers/cpufreq/
amd_freq_sensitivity.ko  pcc-cpufreq.ko
Found it, we’re indeed in powersave mode :
[root@wall] lib # find /proc /sys -name \*cpufreq\*

[root@wall] lib # grep ^ /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor
Availabe CPU frequency governors :
[root@wall] lib # grep ^ /sys/devices/system/cpu/cpu?/cpufreq/scaling_available_governors
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors:performance powersave
/sys/devices/system/cpu/cpu1/cpufreq/scaling_available_governors:performance powersave
/sys/devices/system/cpu/cpu2/cpufreq/scaling_available_governors:performance powersave
/sys/devices/system/cpu/cpu3/cpufreq/scaling_available_governors:performance powersave
Ok, this does affect CPU frequency :
[root@wall] lib # for cpu in /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor ; do echo powersave > $cpu; done

[root@wall] lib # for cpu in /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor ; do echo performance > $cpu; done

Searching for more powa!

Fine, CPUs remain at 1.7 GHz under load, with seldom peaks at 2 GHz – pursuing investigations searching for “more performance” or reactivity :

[root@wall] lib # for thing in /sys/devices/system/cpu/cpu?/cpufreq/* ; do \
      echo `echo $thing|grep -o 'cpu[0-9]'`:`basename $thing`:`cat $thing`:--:$thing ;\
    done |
      column -s: -t

cpu0  affected_cpus                0
cpu0  cpuinfo_cur_freq             1699945
cpu0  cpuinfo_max_freq             3400000
cpu0  cpuinfo_min_freq             800000
cpu0  cpuinfo_transition_latency   4294967295
cpu0  related_cpus                 0
cpu0  scaling_available_governors  performance powersave
cpu0  scaling_driver               intel_pstate
cpu0  scaling_governor             performance
cpu0  scaling_max_freq             3400000
cpu0  scaling_min_freq             800000
cpu0  scaling_setspeed             <unsupported>

Hum… – reading archlinux’s Maximizing performance

Hard-drive read speed seems ok :
[root@wall] lib # hdparm -t /dev/sda

 Timing buffered disk reads: 298 MB in  3.01 seconds =  99.01 MB/sec
Free memory (with 3 Clang jobs running) seems ok :
[root@wall] lib # free -h
             total       used       free     shared    buffers     cached
Mem:          3.7G       3.3G       447M       133M        75M       1.3G
-/+ buffers/cache:       1.9G       1.8G
Swap:         4.0G        18M       4.0G
Reading Linux kernel doc.: cpu-freq/governors.txt

Can’t set the cpuinfo_transition_latency :-/

[root@wall] lib # echo 594967295 > /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency -su: /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency: Permission denied

LLVM build is at 64% – gonna have some coffee – will read some doc. probably…

End of transmission, the morning after, Sept. 15th.