On Sun, 17 Feb 2019, david wrote:
On 2/17/19 1:01 PM, Len Ovens wrote:
- no hyperthread
- etc.
Yet on my i7 laptop, audio works with hyperthreading just fine.
My experience is that HT is ok at 64/2 but starts to have problems at
lower latency. This doesn't matter for most recording where the audio can
be run at 1024/2 but when using the computer as a live synth or guitar
effects unit, it matters. My general thought is that if something matters
at a lower latency... sooner or later it will bite with a "stray" xrun
even at a higher latency.
It is in performance mode, though. I think keeping a steady clock is
more important for RT audio than the number of threads.
In recent intel chips with "Boost", Performance mode means set the cpu
speed to rated speed. However, at higher cpu use the speed will still go
up and down between the limmits of rated speed and max boost speed. Going
up does not seem to be a problem, but going down does. Also, Boost is
temperature controlled... this means that the cpu is running closer to the
maximum temperature and if it gets too close the speed will go below
rated speed to cool down. Temperature control uses cpu time... but the
code is not controlled by the OS and over temperature events tend to do
bad things to audio. So it is worth turning Boost off to give a steady
clock frequency. (I have in the past found that setting speed to 800Mhz
does better audio than "ondemand" at 1.6Ghz) By watching temperatures
while running the cpu(s) at 100% (build Ardour for example) I have found
that I could actually run at a higher speed than preformance by setting
min/max speeds rither than a governor. However, I don't do this because I
know that things like dust and wearing fans will change this over time and
rated speed does give some headroom.
Anyway, I set jack to 16/2 and tweak for (hopefully) no xruns or best
case. Then I am pretty sure I have done the best I can do at higher
latency. (I turn cron off too while recording) I have a PCI audio device,
USB devices will not do 16/2... 16/3 maybe, probably 32/* is a better
target for USB.
--
Len Ovens
www.ovenwerks.net
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