[PD] pd and multi-core processors

Tim Blechmann tim at klingt.org
Wed Apr 7 10:54:05 CEST 2010

>> thanks for the tip. I have no idea how to do that though.
>> I admit not having searched for very long (it's late), but i couldn't
>> find an easy peasy how-to disable frequency scaling,
> on ubuntu usually:
> $ sudo cpufreq-selector -g performance
> I guess this is the same as overriding the sysctl files in:
> /sys/devices/system/cpu/cpuX/cpufreq on modern linuxes.
> I don't know about the default kernel, but in the realtime kernel
> running applications with realtime privileges (for instance pd -rt) and
> dynamic cpu frequency scaling doesn't work well together, so I guess one
> is better off by disabling it. I tend to believe that cpu frequency
> scaling fails to adapt when 'pd -rt' requires it, because Pd has such a
> high priority, even higher than the governor controlling the scaling.
> When using other (low priority) applications, gcc for instance, scaling
> works as expected.

cpu scaling may occur at the level of the operating system and at hardware 
level (controlled by the bios). e.g. some systems will modulate the clock to 
keep the cpu temperature in a certain range, although you are in performance 
mode. this is invisible at the scope of the os, although it will increase 
the worst-case scheduling latency.

tim at klingt.org

May music never just become another way of making money.
  Keith Tippett

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