[PlanetCCRMA] XRUNS and more

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Fri May 13 08:43:36 PDT 2016

On 05/13/2016 05:15 AM, Etienne Rouge wrote:
> Hello,

Hi Etienne,

> I've recently switched back to CCRMA and I'm rather happy with it.
> However I still have xruns when I really shouldn't (powerfull computer
> and reasonnable amount of tracks/effects).
> I've set up PAM…  added "rtc firewire_ohci" to the irq file. Honestly, I
> don't quite understand the few tuts I find online and the fact they are
> not fedora-oriented don't help.
> Is there a crucial step I've missed ? A tutorial I can follow ?

Could you tell us what hardware is this? What software are you running? 
I presume you are running rtirq and you have access to SCHED_FIFO rt 
scheduling in your account.

I have found that for critical low latency work using recent hardware I 
need to disable hyperthreading (the fake cores on Intel processors that 
can't do much) and also set the intel_pstate driver to try to use all 
cores at high speed. Also disable thermald if you are using it (it could 
also be throttling the processors). Maybe this would help?

I have this in a script I run when needed (this is on a four core Intel 
laptop with HT):

# get all processors to run fast all the time...
echo "100" > /sys/devices/system/cpu/intel_pstate/min_perf_pct

# turn off hyperthreading which only makes things worse most of the time
# we do this by turning off cpus that have the same "proc id"
echo 0 > /sys/devices/system/cpu/cpu1/online
echo 0 > /sys/devices/system/cpu/cpu3/online
echo 0 > /sys/devices/system/cpu/cpu5/online
echo 0 > /sys/devices/system/cpu/cpu7/online

Best luck! And let us know how it works out...
-- Fernando

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