[64studio-devel] [Jackit-devel] CPU load reading too high on dual-core and SMP machines?

[Daniel James]

Hi Stéphane,

> Hum... what do you mean by "load as double that which top reports for 
> total CPU load" ?

I mean if I hit the '1' key while running top, it toggles between 
showing the average CPU load across cores or processors, and the load on 
individual cores. So if I had 60% and 20% loads respectively, by default 
top would show 40% and qjackctl would show 80%. If load goes up to 60% 
and 60% respectively, then top shows 60% but qjackctl shows only 20%, 
which is why I concluded that jack must be wrapping after 100%.

> Jack DSP CPU measure the sum of DSP load of all running jack clients

Right, but in my example cases the Jack apps are the only apps consuming 
significant CPU.

> You are supposed to have problems  (= xruns) in the setup you describe 
> since the sum of both processor load exceed 100% and you are running 
> "sequential" jack... Do you have them?

We have users testing ardour with multiple instances of jamin on kernel 
2.6.18. One user with a single-core Sempron 64 ran ardour plus three 
jamins for two hours. 95% CPU load, no xruns. Another user tried the 
same thing on a dual core Athlon 64, and CPU usage was reported by the 
jack apps as 56%. But when the number of jamin instances was increased 
to four, the CPU usage was reported as only 2.5%, and although the 
system kept working, there was indeed the occasional xrun. It seems 
reasonable to assume that the sum of loads was actually 102.5% at this 
point.

> Concerning jackdmp use in a distribution, it seems that Ubuntu studio is 
> testing the possibility, see 
> http://ubuntuforums.org/showthread.php?t=283111

Yes, I saw that thread. We are in a somewhat different situation because 
we have been making releases for 18 months, and are finalising our 
stable 1.0 release, while Ubuntu Studio has yet to be released.

For a future version, it would be great to be able to package both jackd 
and jackdmp in such a way that users could choose which server they 
wanted at runtime, without breaking any of the apps.

Cheers!

Daniel