linuxaudio.org

On 08/05/2012 10:04 PM, Ralf Mardorf wrote:

quoted text
> On Sun, 2012-08-05 at 21:39 +0200, Jeremy Jongepier wrote:

>> Just added this to the LinuxMusicians Wiki:

>> http://wiki.linuxmusicians.com/doku.php?id=system_configuration#cpu_freq...

>

>         "The command in your /etc/rc.local file only works if you

>         disable the ondemand service. On Debian systems:

>

>         sudo update-rc.d ondemand disable

>

>         Another option would be to modify the ondemand init script and

>         rename it to performance:

>

>         sudo sed -i 's/ondemand/performance/g' /etc/init.d/ondemand

>         sudo update-rc.d ondemand disable

>         sudo cp /etc/init.d/ondemand /etc/init.d/performance

>         sudo update-rc.d performance enable"

>

> Last time I used Debian there was a script /etc/init.d/cpufrequtils that

> set up the governor to ondemand. It's not that long ago, so I guess for

> Debian this didn't change. Len of course refers to Ubuntu (Studio).

> AV Linux (Debian) also has got /etc/init.d/cpufrequtils:

>

> "[snip]

> # Set ENABLE to "true" to let the script run at boot time.

> #

> # eg:	ENABLE="true"

> #	GOVERNOR="ondemand"

> #	MAX_SPEED=1000

> #	MIN_SPEED=500

>

> ENABLE="true"

> GOVERNOR="performance"

> MAX_SPEED="0"

> MIN_SPEED="0"

> [snip]"

>

> I once wrote a script to toggle between ondemand and performance, not

> only for the session, but also to keep it for next startup, based

> on /etc/init.d/cpufrequtils.

>

> Regards,

> Ralf

> 

I really wonder why you are all raving about this.
Well, it is hard to generalize but on most modern CPUs + main-boards CPU

frequency scaling is _not_ correlated to audio-dropouts [anymore] and a

non-issue.
The time it takes to change CPU frequencies is very small compared (us)

to [even] low-latency audio (ms). Concerning Hardware, these days,

bus-power-management is most often the cause of xruns on idle systems

followed by SMI.
Disable PCI and/or PCIe power-management in the BIOS and also disable

EIST and C1E halt-states; and, the 'ondemand' governor will works just fine.
If you have an unlimited supply of power and noise of cooling

the system is of no concern: sure, use the 'performance' CPU-freq

governor -- reducing the number of possibilities in complex systems

usually increases reliability... which is indeed a good thing for audio.
ciao,

robin
NB. frequency scaling _can_ be an issue when using jack2 (or tschak) on

a multi-core machine: The total system-load (over all CPUs) may still be

too low for the CPU governor to react, while DSP load is already at the

limit. -- http://rg42.org/oss/jackfreqd/

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