[mythtv] 100% CPU load, consumes 75% Mem

[jrohr]

Since todays pacman -Suy, the mythbackend process on my raspberrypi3 goes will, it is stuck at 100% CPU load, consumes approximately 75% of system memory and if a client connects, it is very very slow to respond and after a short while dumps core or is killed by the kernel because it is out of memory.

Before today, it has been running just fine for two years or so. I downgraded the package again, but this didn't make the process behave, also I empties the database and set mythtv up from scratch, this changed nothing.

There is nothing unusual in the system log, also running mythbackend with the --loglevel=debug flag did not give me any useful information. Therefore, my bug report is rather unspecific at this point. Can someone advise what I have to do to make it more useful?

[ajtucker]

I had the same problem after an upgrade last week, running on a BananaPi. The Myth backend process gradually uses up all memory until it gets killed.

I spent a while downgrading packages until Myth worked again using the downgrade script. I think it's the qt 5.8 upgrade that's the culprit, as after I downgraded all qt5-* packages to 5.7.1-1, Myth backend works again.

[jrohr]

Indeed, downgrading all qt packages to 5.7 did the trick. I am not sure, whether one should report this issue to the mythtv developers or the Qt developers or both, because, while it is great to have it fixed for now, it would be even better to have it permanently fixed.

[jrohr]

I have now submitted a bug report, they say:

$this->bbcode_second_pass_quote('', 'T')he highest version of QT available on Ubuntu is QT 5.7 on the pre-release Ubuntu 17.04 version, so it is likely that MythTV has not been tested with 5.8 on any platform. It is possible that this problem not exclusive to raspberry pi or banana pi.

[ajtucker]

Thanks for submitting a bug report!

I did attempt to run up a minimal test case on a local docker container to see whether the same problem occurs on x86_84, but haven't got too far yet. I was hoping to do some gdb style debugging, as setting verbose logging on mythbackend with qt5.8 on ARM didn't show anything peculiar.

A quick look over the the QT bug reports doesn't show anything obvious either.

This is a bit of a blocker for MythTV on Arch and at the moment Arch seems to be the only distribution packaging qt5.8, so perhaps we should raise an issue on the Arch bugzilla?