[mythtv-users] Mythbackend using 100% CPU when idle

Chris Weiland hobbiticus at gmail.com
Thu Feb 1 19:32:48 UTC 2007

I'm having a very strange problem with mythbackend in that sometimes it will
use up 100% of my CPU when doing absolutely nothing.  It does not happen
right away, but only after running for between an hour to a day or so.  So,
I can't really reproduce it quickly, and I don't know what is to blame.
Here's a concise list of symptoms:

-100% CPU usage when not doing any recording/playback
-About 40-50% of the CPU is being used by "Sys" (as in Usr/Sys/Nice/Idle)
-No disk or swap activity
-If I happen to be recording something on my tuner card at the time, the
problem doesn't seem to interfere, which means that when I play back the
recording, there are no skips/studders in the audio or video
-The rest of the system is not very responsive (i.e. web browsing, or
watching recordings)
-The problem will temporarily go away if I restart the mythbackend daemon
-No questionable entries in the backend's logfile near the time of the

I have the slightest suspicion that it may have something to do with
mythfilldatabase being autorun (specifically when it finishes), but I've
only noticed this once, which could easily be a coincidence.  Manually
running mythfilldatabase has never caused this problem in the 30 or so times
I've done it.

My system:
Asus M2N-E motherboard (nForce 570 chipset)
AMD64 3800+
2 Gb ram
GeForce 7600GT (PCI-E)
SoundBlaster Audigy 2 ZS
pcHDTV 5500 tuner
Debian echt (testing), using debian package from www.debian-multimedia.org's
apt source for MythTV.  I believe this was created from an svn snapshot from
early december.
Kernel 2.6.20-rc5 preempt (tried with/without APIC/IO-APIC with the same
I'm still running a 32 bit kernel.

I'm running mythtv on my main machine as a "dry run" before making a
dedicated box for it, so to make recordings more reliable, I'm running the
backend at nice level -2.

Any ideas?
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