On Thu, Jul 02, 2015 at 12:53:59PM +0200, Peter Zijlstra wrote: > On Thu, Jul 02, 2015 at 07:25:11AM +0800, Yuyang Du wrote: > > And obviously, the idle balancing livelock SHOULD happen: one CPU pulls > > tasks from the other, makes the other idle, and this iterates... > > > > That being said, it is also obvious to prevent the livelock from happening: > > idle pulling until the source rq's nr_running is 1, becuase otherwise we > > just avoid idleness by making another idleness. > > Well, ideally the imbalance calculation would be so that it would avoid > this from happening in the first place. Its a 'balance' operation, not a > 'steal everything'. > > We want to take work -- as we have none -- but we want to ensure that > afterwards we have equal work, ie we're balanced.
Agreed, I think this is the true problem. See my other reply. > > So clearly that all is hosed. Now Morten was looking into simplifying > calculate_imbalance() recently. Yes. I'm held up doing other stuff at the moment, but I think calculate_imbalance() needs some attention and I'm planning on looking at that next. -- 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/
