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

david gnome at hawaii.rr.com
Thu Jan 28 06:26:38 CET 2021

On 1/27/21 8:02 AM, Len Ovens 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.
Intel doesn't run at top speed "forever". Fastest clock I've got from my 
nominal 5GHz-max i9 in my Dell XPS 15 is 4.7GHz. Intel runs clock speed 
until thermals say "Slow down." If you're talking about a laptop, the 
specific laptop's ability to dissipate heat is the controlling factor. 
I'm not sure that Intel thermal control is anywhere within reach of BIOS 
and OS software.

> 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.

It and clock are good indicators.

David W. Jones
gnome at hawaii.rr.com
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"My password is the last 8 digits of π."

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