Please help.Spontaneous but persisting slowdown making cab unusable Ubuntu 12.04

[Davros]

Hello.

Finally got my cabinet built and up and running for a few months now.  A massive thank you to everyone here at BYOAC for aiding me on the transcendental voyage to reach the Nirvana that is owning one's own fully functional Mame cabinet.
On the functionality front ... that part has recently let me down. Games are now running at  a speed that makes them unplayable. Contra runs low 50

Using Mame149, compiled from source for nag/hi-score. Running Ubuntu 12.04 on Optiplex 745. 2 Ultimarc 360s and Happ trackball

At first I thought this may be a buffering issue, that is, faulty controller flooding the system and overloading. When this happened once before while trying to isolate issue, unplugging everything seemed to fix. This time no luck.
It is worth noting that movies play absolutely fine with good sound on the computer. Would guess that this would suffer too if it was a hardware fault.

Has this happened to anyone else? If anyone has any suggestions I would be very grateful.

Frustrated in Kent

[General_Faliure]

I think Ubuntu has way too much stuff you don't need for an arcade cab, that might slow it down.
I use Lubuntu 14.04 now which is a much lighter weight system.
My first mainboard was an athlon Xp 2100, 750 Mb mem and an Ati 9250, even then it worked fine.
You can try using monitoring software, like top, to see what's hogging the system.
The best option would be switching to Lubuntu 14.04

[Davros]

Thanks for the response General_Failure.
I hear you. I think it is good advice. The thing is it has been working fine for months.
I am hoping to hear that there is a problem with the latest SDL release or something equivalent. (And of course an accompanying workaround)

There are no processes running on the machine except Mame.
I am not experienced enough in Linux to check/understand what daemons could be causing the problem.
As I said, I would assume playing video would consume the same resources as Mame. No problems there.

[Davros]

Well....Rebooting with no USB devices whatsoever (including keyboard!!!) plugged in meant all games returned to running near 100%.
Plugged in all controls, rebooted and all back to working just fine. Hurrah!

Not sure what was going on.
I wouldn't expect this behaviour. No amount of rebooting was solving the problem.
I am sure there is an easy explanation.
Nevertheless, hopefully this post helps someone, sometime.

Happy gaming!