R13B SMP Migration logic

原文地址：http://erlang-factory.com/upload/presentations/105/KennethLundin-ErlangFactory2009London-AboutErlangOTPandMulti-coreperformanceinparticular.pdf

Migration logic

* Strive to keep the maximum number of run able
processes equal on all schedulers

* Load balancing is performed by the scheduler that
first reaches its max limit of reductions.
   1. Collect statistics about the maxlength of all
  schedulers run-queues
   2. Calculate the average limit per run-queue/prio and
setup migration paths
  3. Give away jobs from schedulers over the limit,
Take jobs to schedulers under the limit

* Migrations occurs when the scheduler has finished
a job and goes on until the limit is reached or a new
loadbalancing takes place.

*  There is also work-stealing , which occurs when a
scheduler gets an emty run-queue

* Running on full load or not!

If all schedulers are not fully loaded, jobs will be
migrated to schedulers with lower id’s and thus
making some schedulers inactive.

这个就是为什么R13的多处理器支持强好多的原因。