F14 cpuspeed / ondemand broken?

[Richard Shaw]

On Fri, Dec 24, 2010 at 12:24 AM, Steven Haigh <netwiz at crc.id.au> wrote:
> On 24/12/2010 4:59 PM, Steven Haigh wrote:
>> I've been trying to nut out an issue with cpuspeed on a Fedora14 box...
>>
>> It seems when cpuspeed is started, it clocks the frequency back to the
>> lowest available (350Mhz in my case), and there it stays.
>>
>> If I do something to create CPU load ( while true; do true; done ) then
>> the CPU fails to be clocked back up to max frequency. In fact, no matter
>> what I do on that box the CPU doesn't move from 350Mhz...
>>
>> To get the system back to 2.8Ghz I need to rmmod the p4-clockmod module.
>>
>> I thought this might have been something silly with the thresholds so I
>> set UP_THRESHOLD and DOWN_THRESHOLD manually in /etc/sysconfig/cpuspeed
>> - however then when starting cpuspeed I see:
>>
>> # /etc/init.d/cpuspeed restart
>> Disabling performance cpu frequency scaling: [ OK ]
>> /etc/init.d/cpuspeed: line 86:
>> /sys/devices/system/cpu/cpu0/cpufreq/ondemand/up_threshold: No such file
>> or directory
>> /etc/init.d/cpuspeed: line 86:
>> /sys/devices/system/cpu/cpu1/cpufreq/ondemand/up_threshold: No such file
>> or directory
>> Enabling ondemand cpu frequency scaling: [ OK ]
>>
>> Kernel version is:
>> # cat /proc/version
>> Linux version 2.6.35.6-45.fc14.i686
>> (mockbuild at x86-16.phx2.fedoraproject.org) (gcc version 4.5.1 20100924
>> (Red Hat 4.5.1-4) (GCC) ) #1 SMP Mon Oct 18 23:56:17 UTC 2010
>>
>> Anyone have any ideas on this? :\
>>
>
> This gets even more interesting!
>
> # cpufreq-info
> cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009
> Report errors and bugs to cpufreq at vger.kernel.org, please.
> analyzing CPU 0:
>   driver: p4-clockmod
>   CPUs which run at the same hardware frequency: 0
>   CPUs which need to have their frequency coordinated by software: 0
>   maximum transition latency: 10.00 ms.
>   hardware limits: 350 MHz - 2.80 GHz
>   available frequency steps: 350 MHz, 700 MHz, 1.05 GHz, 1.40 GHz, 1.75
> GHz, 2.10 GHz, 2.45 GHz, 2.80 GHz
>   available cpufreq governors: ondemand, userspace, performance
>   current policy: frequency should be within 350 MHz and 2.80 GHz.
>                The governor "performance" may decide which speed to use
>                within this range.
>   current CPU frequency is 2.80 GHz (asserted by call to hardware).
> analyzing CPU 1:
>   driver: p4-clockmod
>   CPUs which run at the same hardware frequency: 1
>   CPUs which need to have their frequency coordinated by software: 1
>   maximum transition latency: 10.00 ms.
>   hardware limits: 350 MHz - 2.80 GHz
>   available frequency steps: 350 MHz, 700 MHz, 1.05 GHz, 1.40 GHz, 1.75
> GHz, 2.10 GHz, 2.45 GHz, 2.80 GHz
>   available cpufreq governors: ondemand, userspace, performance
>   current policy: frequency should be within 350 MHz and 2.80 GHz.
>                The governor "performance" may decide which speed to use
>                within this range.
>   current CPU frequency is 2.80 GHz (asserted by call to hardware).
>
> Ok, so it thinks its using the performance governor - even though the
> config files for cpuspeed say to use ondemand..
>
> # cpufreq-set -g ondemand
> # echo $?
> 0
>
> Now it should have set ondemand as the governor.
>
> # cpufreq-info | grep governor
>   available cpufreq governors: ondemand, userspace, performance
>                The governor "performance" may decide which speed to use
>   available cpufreq governors: ondemand, userspace, performance
>                The governor "performance" may decide which speed to use
>
> Interesting. No change at all.

I wish I could find the site where I got this information as my
recollection of it is a bit hazy but part of your problem may be that
the p4-clockmod and ondemand are more or less incompatible. I remember
reading something on kerneltrap or something. Basically the latency of
changing frequencies are so bad with p4-clockmod that ondemand gives
up on it or something like that. I think I could force it to work on
my Celeron based EEEPC by manually setting the governor something like
this[1]:

---
Using Frequency Scaling Governors

You can get a list of available governors with (as root):
# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
conservative ondemand powersave userspace performance

Note: If the governors are compiled as modules, load them first:
# modprobe cpufreq_performance cpufreq_ondemand cpufreq_conservative
cpufreq_powersave cpufreq_userspace

Now we set our governor: What is our current governor?
# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
userspace

Set new governor and watch if it has changed
# echo conservative > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
conservative

Congrats! Your governor is active.
You may set the governor in your rc.local, to make it used on every boot.
---

Richard

[1] http://www.thinkwiki.org/wiki/How_to_make_use_of_Dynamic_Frequency_Scaling