On Thu, Jul 02, 2015 at 12:44:55PM +0100, Morten Rasmussen wrote: > 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.
Yes, this is agreed at all time. Like I said load_balance() (for idle balancing) should compute the right imbalance and move a fair amount, to achieve we are balanced. Whatever is wrong in how much computed and moved "right imbalance" is should be fixed anyway. But still, I think, even with the above, in idle balancing, pulling until the source rq's nr_running == 1 is not just "a short term fix", but should be there permanently acting like a last guard with no overhead, why not. > > > > > 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. Thanks, Yuyang -- 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/
