On Sun, 2010-12-19 at 11:19 +0200, Avi Kivity wrote:
What if: we test that both tasks are in the same thread group, if so,
use cfs_rq->next to pass the scheduler a HINT of what you would LIKE to
happen. If the current task on that rq is also in your group, resched
it, then IFF the task you would like to run isn't too far right, it'll
be selected. If the current task is not one of yours, tough, you can
set cfs_rq->next and hope it doesn't get overwritten, but you may not
preempt a stranger. If you happen to be sharing an rq, cool, you
accomplished your yield_to(). If not, there's no practical way (I can
think of) to ensure that the target runs before you run again if you try
to yield, but you did your best to try to get him to the cpu sooner, and
in a manner that preserves fairness without dangerous vruntime diddling.
Would that be good enough to stop (or seriously improve) cpu wastage?