Re: jerks

[David Olofson <david@olofson.net>]

On Thursday 08 December 2005 18.41, Glenn English wrote:
[...]
> Every few seconds, at seemingly random times, everything freezes for
> ~50ms. Even the mouse. Sometimes. Reliable at the first card moved
> in Aisle Riot Solitaire and when Jack is running. Often when I'm
> typing email (chars don't get from the keyboard to the screen).
[...]

This reminds a bit of something I saw when I made some RTAI latency 
tests on the Mini-ITX motherboards we're putting in our rheometers. I 
would get random latency peaks of anything from a few hundred µs 
through tens of ms.

Turns out the integrated ethernet implementation is a slightly broken, 
and has the interface send interrupts to the CPU even if you disable 
it in the BIOS! Linux "handles" it without freezing indefinitely, but 
even RTAI hard RT kernel threads are locked out for a moment every 
now and then.

Solution: I just installed the driver for the NIC!

We use ethernet for communicating with the instruments anyway, but as 
this project haven't been enough of a PITA already, I just *had* to 
test the RT performance *first*, just so I could discover this scare- 
the-h*ll-out-of-control-engineers special feature... :-D


So, bottom line: Never trust "disabled" PCI devices.


//David Olofson - Programmer, Composer, Open Source Advocate

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