AMD Athlon64 cool'n quiet - questions

[James Wilkinson]

Alexander Volovics wrote:
> The 'AMD Athlon64 qool'n quiet - how?' thread reminded me that there
> are some questions that I would like to ask about 'cool/quiet',
> 'cpufreq/cpuspeed' and/or 'powernow-k8'.
> 
> (I am running FC3-x86_64 on a MSI K8N Neo2 Platinum mobo with AMD64 3500+).
> 
> 'dmesg' shows the following:
> powernow-k8: Found 1 AMD Athlon 64 / Opteron processors (version 1.00.09e)
> powernow-k8:    0 : fid 0xe (2200 MHz), vid 0x2 (1500 mV)
> powernow-k8:    1 : fid 0xc (2000 MHz), vid 0x6 (1400 mV)
> powernow-k8:    2 : fid 0xa (1800 MHz), vid 0xa (1300 mV)
> powernow-k8:    3 : fid 0x2 (1000 MHz), vid 0x12 (1100 mV)
> 
> However I have only ever seen 2 freqencies in use: 1000 and 2200.
> 
> This could because 1800/2000 are excluded from use somewhere or
> because they are 'transient states', only used when switching from
> 1000 to 2200.
> 
> If 'cpuspeed' is responsible for this "exclusion" of 1800 and 2000
> it doesn't seem to be configured in /etc/cpuspeed.conf.
> (Or can the OPTS entry be used for this?)
> 
> Can somebody explain this phenomenon.

How to see intermediate speeds in use (my CPU is a 3200+, so 2000 is its
normal state, and it only has 1800 as an intermediate speed):

 * Open two xterms on a basically idle system.

 * Become root in one of them (you need to be root to read the current
   speed through sysfs).

 * Run
[root at kendrick ~]# cd /sys/devices/system/cpu/cpu0/cpufreq
[root at kendrick cpufreq]# while true ; do cat cpuinfo_cur_freq ; sleep 1 ; done

   It will keep printing the speed in kHz.

 * In the other xterm, run
dd if=/dev/zero of=/dev/null
   (which is a nice do-nothing CPU eater). Watch the speed in the root
   x-term go to max.

 * Kill the dd job with control-C.

 * Watch (in my case, 1800000) an intermediate speed appear for a couple
   of seconds in the root xterm.

 * Kill the while loop with control-C.

I don't know about you, but most of my computer usage tends to be things
like surfing the web, writing e-mails, or listening to music. That's
stuff you can do perfectly well on a 500 MHz computer. You don't need
more than 1 GHz of Athlon 64 power, so the system keeps clock speed down
to 1 GHz.

The rest of what I do on the computer is eye-candy stuff (like 3D
stuff), which takes what processor power it can get, or compiles,
transcoding, and the like, which take as long as they need to take. In
both those cases, the system can make use of 2 GHz of power, and sets
the processor to full speed.

James.
-- 
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