[Bdi4emc-help] Quickstep driver

Matt Timmermans matt at timmermans.org
Mon Feb 13 05:47:37 CET 2006

Hi Doug,

Yes, it's still all real-time.

To measure CPU usage, I just ran bogomips in user space.  This tells me how 
much CPU is left over after all the higher priority tasks take their cut. 
If M is the score when the system is unloaded, or reported during boot, and 
m is the score when EMC is up and doing a rapid move, I know that the 
fraction of CPU consumed by the real-time tasks is <= (M-m)/M.

Uncertainty remains about just how fast you can go, however, because 
quickstep's critical work isn't quite evenly distributed across PERIODs.  I 
don't think it's too far off, though.  On a slower machine, I guess that 
it's probably safe to decrease PERIOD until the real-time work eats up half 
the CPU.  A really fast machine may hit some limit in the capabilities of 
the interrupt hardware first.


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