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

Will Godfrey willgodfrey at musically.me.uk
Wed Jan 27 19:17:09 CET 2021

On Wed, 27 Jan 2021 10:02:48 -0800 (PST)
Len Ovens <len at ovenwerks.net> wrote:

>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.

FWIW I'm running an earlier Ryzen5 here at 32 frames, mostly with Rosegarden and
Yoshimi, using quite complex patches, and averaging 8 active channels at once. I
don't see any Xruns. I do see the occasional one if I do things like load a full
patch set over a running program.

Will J Godfrey
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.

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