[PD] urgent - cpu going to 100% / top weirdness

Damian Stewart damian.ml at frey.co.nz
Sun Feb 8 20:31:44 CET 2009


i'm setting up for an exhibition in Madrid that opens on Tuesday (it's 
called VIDA and it's at Matadero Madrid, come down if you're in town.)

so, i'm trying to track down a strange issue with Pd jumping to 100% cpu
periodically, once every 15 seconds, when i run another cpu-intensive task.
i'm running Pd 0.40-2, installed via apt-get on Ubuntu 8.04. (i have the
same issue with the Pd-extended 0.40-3 .deb from the puredata.info
website). this is on a dual-core Pentium-D 3GHz cpu. i'm using ALSA with an
MAudio Delta 66 card. (linux is *so* not ready for multichannel audio
unless you've got a high end RME device, but that's another story).

if i start up top, and just run pd, it chugs along fine. the cpu usage line
at the top edge of the screen in top stays around 20%us, with around 80%
idle time. and the entry for Pd gives a CPU usage of 63% (i don't
understand what these two values mean or why they differ)

if i then start up a cpu-intensive graphical task that sits around 100% but
is only single-threaded, the weirdness begins. in top, the total CPU usage
line jumps up to 70%. in the listing of processes below, the cpu-hungry
graphical task sits on around 97%, but the Pd process is now down to 36%.
after running for around 30 seconds, the Pd process jumps up to 100%,
totally killing the framerate on the cpu-hungry graphical task. it stays
like this for 10 or so seconds, then drops back down to 36%, before
repeating the cycle again after another 20-30 seconds.

i tried running pd with -nogui and -rt -- no change. i also tried running
pd with niceness -10 and the graphical task with niceness 10 -- again, no

so, questions. first, wtf? why is top reporting a lower cpu usage in the
second scenario than in the first?

second: how can i stop this?

third: it's possible this is being caused by an almost-infinite loop in one
of my patches. how can i profile them to test this?


damian stewart | skype: damiansnz | damian at frey.co.nz
frey | live art with machines | http://www.frey.co.nz

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