On Thu, Apr 24, 2014 at 09:53:37AM -0700, Jason Low wrote: > > So I thought that the original rationale (commit 1bd77f2d) behind > updating rq->next_balance in idle_balance() is that, if we are going > idle (!pulled_task), we want to ensure that the next_balance gets > calculated without the busy_factor. > > If the rq is busy, then rq->next_balance gets updated based on > sd->interval * busy_factor. However, when the rq goes from "busy" > to idle, rq->next_balance might still have been calculated under > the assumption that the rq is busy. Thus, if we are going idle, we > would then properly update next_balance without the busy factor > if we update when !pulled_task. >
Its late here and I'm confused! So the for_each_domain() loop calculates a new next_balance based on ->balance_interval (which has that busy_factor on, right). But if it fails to pull anything, we'll (potentially) iterate the entire tree up to the largest domain; and supposedly set next_balanced to the largest possible interval. So when we go from busy to idle (!pulled_task), we actually set ->next_balance to the longest interval. Whereas the commit you referenced says it sets it to a shorter while. Not seeing it. So the code as modified by Ingo in one of the initial CFS commits, will move the ->next_balance time ahead if the balance succeeded (pulled_task), thereby reflecting that we are busy and we just did a balance so we need not do one again soon. (we might want to re-think this if we really make the idle balance only pull 1 task max). Of course, I've now gone over this code 3 times today, so I'm terminally confused. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
