Hi Vincent, On 09/03/2014 10:28 PM, Vincent Guittot wrote: > On 3 September 2014 14:21, Preeti U Murthy <pre...@linux.vnet.ibm.com> wrote: >> Hi, > > Hi Preeti, > >> >> There are places in kernel/sched/fair.c in the load balancing part where >> rq->nr_running is used as against cfs_rq->nr_running. At least I could >> not make out why the former was used in the following scenarios. >> It looks to me that it can very well lead to incorrect load balancing. >> Also I did not pay attention to the numa balancing part of the code >> while skimming through this file to catch this scenario. There are a >> couple of places there too which need to be scrutinized. >> >> 1. load_balance(): The check (busiest->nr_running > 1) >> The load balancing would be futile if there are tasks of other >> scheduling classes, wouldn't it? > > agree with you > >> >> 2. active_load_balance_cpu_stop(): A similar check and a similar >> consequence as 1 here. > > agree with you > >> >> 3. nohz_kick_needed() : We check for more than one task on the runqueue >> and hence trigger load balancing even if there are rt-tasks. > > I can see one potentiel reason why rq->nr_running is interesting that > is the group capacity might have changed because of non cfs tasks > since last load balance. So we need to monitor the change of the > groups' capacity to ensure that the average load of each group is > still in the same level > >> >> 4. cpu_avg_load_per_task(): This stands out among the rest as an >> incorrect usage of rq->nr_running in place of cfs_rq->nr_running. We >> divide the load associated with the cfs_rq by the number of tasks on the >> rq. This will make the cfs_rq load look smaller. > > This one is solved in the consolidation of cpu_capacity patchset
Sorry, but I don't see where in your patchset you have addressed this issue. Can you please point out the patch? 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/
