Re: [Condor-users] CPU Affinity Controlling

[Greg Thain <gthain@xxxxxxxxxxx>]

> Can you describe how CPU affinity control works?
>   

The documentation is lagging on this feature, but here's a quick 
overview.  It only works on Windows and recent linux versions.

If you haven't changed NUM_CPUS to support extra slots, and you want one 
CPU core per Condor slot, just set

ENFORCE_CPU_AFFINITY = true

in the condor_config file on the startd side, and each slot will be 
bound to a single CPU core.  If affinity is being set, and D_FULLDEBUG 
is on, there will be a line indicating this printed to the StarterLog. 

If you want more control, you can set ENFORCE_CPU_AFFINITY=true and set 
the CPU affinities per slot by saying, for example:

SLOT1_CPU_AFFINITY=0,1
SLOT2_CPU_AFFINITY=1,2,3

which means that jobs on slot1 run on cores 0 and 1.  Note that slots 
are enumerated with 1 based numbering and CPU cores with zero based.

We are interested in feedback and the results of using these settings in 
real world job mixes.  Our belief is that enforcing CPU affinity will 
increase fairness and potentially decrease overall throughput.  The 
Linux process scheduler is said to be designed to share priority when a 
parent process forks, so that spawning many processes doesn't improve 
your effective priority.