[LITMUS^RT] IPI vs. Cache Affinity

[Glenn Elliott]

I've been getting more acquainted with the latest litmus code and I see that GSN-EDF/C-EDF prefer to schedule a task on the local CPU if the CPU is available.  This avoids an IPI.  However, this may result in higher cache migration costs because this scheduling decision is made before checking CPU affinity.

Are IPI costs (significantly) higher than cache affinity loss?  Are we making the assumption that affinity has already been lost due to cache polluters?  Do we have empirical data to support the current implementation?  I'm not arguing in favor of one method or the other---I am just interested in the motivations behind the changes.

Thanks,
Glenn