PS: Default CPU frequency scaling issue

[Ralf]

On Sat, 2011-05-21 at 11:05 +0200, Ralf wrote:
> Hi :)
> 
> today I installed Ardour3, perhaps Paul Davis recommendation is more
> important than mine [1].
> 
> My Kernel is set to use 'performance' as default setting for the CPU
> frequency scaling [2]. If I start a GNOME session it's set to "ondemand"
> automatically.
> 
> I'm starting sessions by a script, unfortunately some Ubuntu installs
         AUDIO SESSIONS
> need a "sudo" before "cpufreq-selector -g performance", while others are
> not fine with the "sudo", some other installs, e.g. Suse do need a
> different command, ok, Suse keeps "performance" ;). Older Ubuntu
> installs needs a SUID bit set ;).
> 
> So I need to write a script checking for the distro + distro version or
> I need to set it by the panel each time after starting a GNOME session,
> or I need to add aliases to the shells. At the moment I'm doing it by
> the panel.
> 
> The right way should be, that Ubuntu Studio GNOME does use the kernel's
> default. This needs a fix. The DE shouldn't try to be smarter than the
> user!
> 
> Btw. using "ondemand" might safe 1W on modern 40/50W CPUs. This isn't
> much pollution projected onto Linux audio users. I'm using "ondemand"
> when not making music, but the default should be "peformance". Note that
> some people are working on a Jack frequency scaling!
> 
> Cheers!
> 
> Ralf
> 
> 
> 
> 
> [1]
> $ ./install.sh
> 
> Welcome to the Ardour installer
> 
> Sat May 21 10:32:35 CEST 2011
> Architecture is x86
> [snip]
> 
> System failed the quick sanity check... Looking for the cause
> 
> !!! WARNING !!! - Your system seems to use frequency scaling.
> This can have a serious impact on audio latency. You have two choices:
> (1) turn it off, e.g. by chosing the 'performance' governor.
> (2) Use the HPET clocksource by passing "-c h" to JACK
> (this second option only works on relatively recent computers)
> 
> Press ENTER to continue:^C
> $ ./install.sh
> 
> Welcome to the Ardour installer
> 
> Sat May 21 10:36:01 CEST 2011
> Architecture is x86
> Unpacking bundle for x86
> 
> Checking system libs to see if they are compatible with Ardour.
> 
> 
> Found existing Ardour installation.
> Do you want to run the
> uninstaller /opt/Ardour-3.0alpha3_9210-dbg.uninstall.sh ? [y/n]: n
> 
> Installing Ardour 3.0alpha3 built from 9210 in /opt
> 
> mkdir: cannot create directory `/opt/Ardour-3.0alpha3_9210-dbg': File
> exists
> Adding Ardour to the applications menu
> 
> Creating a desktop link for Ardour
> 
> Copying uninstall script to /opt
> 
> 
> Checking to see if Jack is installed
> 
> Jack OK
> 
> Cleaning up
> 
> !!! Install Complete !!!
> 
> Press ENTER to exit installer:
> 
> [2]
> $ cat config-2.6.33.9-rt31 | grep CONFIG_CPU_FREQ_DEFAULT_GOV
> CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
> # CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set
> # CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set
> # CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set
> # CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE is not set