One of the biggest challenges in a multiprocessing environment
is to distribute evenly the work across available processors. When
a process is created, it is set to run initially on the same SPU
as the parent, because a forked process is likely to use some of
the same context as the parent. By launching on the same processor,
the system takes advantage of previously cached data and avoids
cache coherency performance issues.
In a multiprocessor environment, each SPU has a separate run
queue. Once a thread is put on a run queue (with setrq())
for a certain processor it remains there until removed with remrq().
When a process is ready to run, the processor to which it is scheduled
is based on the kthread.kt_spu_wanted
field.
Of major concern is to keep the relative load balanced among
processors. To do this, each iteration of schedcpu() calls
the routine mp_spu_balance().
Additionally, any spu in an idle state may attempt to steal
threads from other processors. This is done by the kernel routine
find_thread_other_spu().
