[Cbe-oss-dev] what's the expected behaviour for nosched contexts?

[Christoph Hellwig]

Currenly SPU_CREATE_NOSCHED has the following affects on spu contexts:

 (1) they're excluded from coredumps
	- why?

 (2) it selects a different set of files in the context directory
	- probably makes sense, it might be better to have a nosched
	  flag in the tree_descr to make sure they are kept in sync

 (3) creating requires CAP_SYS_NICE
 	- makes sense

 (4) we do some accouting for the number of nosched spus, and
     we ignore them when making affinity placement decisions

What's lacking is any affect on scheduling.  What are the semantics
SPU_CREATE_NOSCHED should have on scheduling?  We should probably avoid
involuntary context switches.  What about voluntary context switches,
e.g. for spu_acquire_saved?  Are they allowed?  Should we ensure they
get switched back to the same spu?  Can we use the spu for another
context in the meantime?