Hi Vincent, On 05/23/2014 09:22 PM, Vincent Guittot wrote: > The imbalance flag can stay set whereas there is no imbalance. > > Let assume that we have 3 tasks that run on a dual cores /dual cluster system. > We will have some idle load balance which are triggered during tick. > Unfortunately, the tick is also used to queue background work so we can reach > the situation where short work has been queued on a CPU which already runs a > task. The load balance will detect this imbalance (2 tasks on 1 CPU and an > idle > CPU) and will try to pull the waiting task on the idle CPU. The waiting task > is > a worker thread that is pinned on a CPU so an imbalance due to pinned task is > detected and the imbalance flag is set. > Then, we will not be able to clear the flag because we have at most 1 task on > each CPU but the imbalance flag will trig to useless active load balance > between the idle CPU and the busy CPU.
Why do we do active balancing today when there is at-most 1 task on the busiest cpu? Shouldn't we be skipping load balancing altogether? If we do active balancing when the number of tasks = 1, it will lead to a ping pong right? Regards Preeti U Murthy -- 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/
