[LAU] Discussion: Future CPU-technology vs. realtime audio?

[Len Ovens]

On Wed, 27 Jan 2021, Michael Jarosch wrote:

> As soon as frequency switching was introduced we LAU were told, not to 
> use it to save xruns. And as far as I can tell, the rule still valid. Is 
> there a chance in the future that we can stop thinking about it, because 
> it just won't matter? Are we forced blowing loads of energy or do we 
> spent too much time in sluggish UEFI menus?

It depends. Setting jack to frame size 64 or lower has in my experience 
shown xruns with frequency switching. This includes Intel's "Boost" 
setting which is not turned off by setting performance. There seems to be 
no problem when the speed goes up but I often see an xrun when the speed 
goes down (just at speed change).

However, Intel has been doing speed switching in the CPU for a while now 
and we are still able to set a steady speed with that on the fly. So with 
the AMD it may be similar. It may still be possible to set an upper and 
lower speed limit. What they do not say, is that the advertized speed may 
not be usable in steady state. With the Intel, the advertized speed can be 
set for all cores and run that way at 100% core use and run forever 
without over heating. AMD tends to advertize a cpu speed based on some 
cores running slower and the cpu managing heat by slowing some cores down. 
In this case one will have to experiment to find out what speed can be 
safely run on all cores without over heating and use that speed for audio. 
Hopefully this can be set on the fly.

Another comment of "blowing loads of energy" with performance mode. It was 
actually found that the old "ondemand" governor actually used more power 
than "performance" in many cases. Ondemand has to wake up every once in a 
while to see what is happening, but in performance mode the core can go to 
an idle state. The newer intel powersave mode does not have this problem 
but AMD (although they started work on their own governor for linux) can 
only use ondemand.

The easiest way to see power use is to watch core temperature... all power 
used ends up as heat.

--
Len Ovens
www.ovenwerks.net