K 10
svn:author
V 3
jhb
K 8
svn:date
V 27
2011-11-16T17:48:05.267513Z
K 7
svn:log
V 602
Partially MFC 218195, 218424, and 221829:
- Put the general logic for being a CPU hog into a new function
  should_yield().
- Encapsulate the common case of check-and-yield into a new function
  maybe_yield().
- Add kern_yield() as a more generic version of uio_yield() and reimplement
  uio_yield() in terms of kern_yield().

To preserve the ABI of struct thread, should_yield() in 8 continues to
use PCPU_GET(switchticks) rather than the td_swvolticks added in 9.  Also,
existing users of uio_yield() are left unchanged.  Instead, the routines
are merely added for use by new code.

Reviewed by:	mdf

END