On 1/27/21 8:17 AM, Will Godfrey wrote:
On Wed, 27 Jan 2021 10:02:48 -0800 (PST)
Len Ovens <len@xxxxxxxxxxxxx> 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.
Ages ago, I forced my old i7 laptop (with USB2) to performance mode (via
command lines on bootup, IIRC) and it stayed there, running at 2.4GHz
all the time. Occasional xruns but nothing that interfered with anything.
I've not touched the performance modes on my current i9 laptop. It
ranges from sub-1GHz to 4.5GHz clock, as needed. I think I've seen
fewer xruns than I had on the i7 with an RT kernel. I don't know if
that's related to the fact that the i9 laptop uses USB-C/USB3.2 and I
have almost everything (including the Ethernet network connection) going
through an external Thunderbolt/USB-C dock. USB soundcard and USB MIDI
connection also go through the dock.
I'm not running an RT kernel on the i9. I don't know how USB3.2/USB-C
handles interrupts vs how USB2 handled them, or if that would have an
impact on things.
Audio-wise, I don't do anything anywhere near as ambitious as Will does.
--
David W. Jones
gnome@xxxxxxxxxxxxx
authenticity, honesty, community
http://dancingtreefrog.com
"My password is the last 8 digits of π."
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