flags that control the degree of CPU resource sharing:
    - yield leftover quantum to others
    - keep cache contents

in a sense, we'd really like these to be tied to categories: e.g. any
thread tainted in a category will necessarily be forced to not yield
its leftover time quantum to others, and to flush cache contents.

but associating it with resources may be a reasonable alternative,
since the owner of the category is the one that must provide any
resources for this tainted execution in the first place.

so, these flags get set on containers that provide CPU resources, and
a thread can also voluntarily ask its CPU resources to be subject to
stronger constraints (e.g. a thread that owns a category may want to,
at its discretion, flush cache contents on context switch).  this is
simply an optimization to avoid the need to create dummy containers
and shuffle owner threads around.