Messages in this thread | | | Date | Thu, 1 Aug 2013 16:48:58 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 18/18] sched: Swap tasks when reschuling if a CPU on a target node is imbalanced |
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On Thu, Aug 01, 2013 at 10:29:58AM +0530, Srikar Dronamraju wrote: > > @@ -904,6 +908,8 @@ static int task_numa_find_cpu(struct task_struct *p, int nid) > > src_eff_load *= src_load + effective_load(tg, src_cpu, -weight, -weight); > > > > for_each_cpu(cpu, cpumask_of_node(nid)) { > > + struct task_struct *swap_candidate = NULL; > > + > > dst_load = target_load(cpu, idx); > > > > /* If the CPU is idle, use it */ > > @@ -922,12 +928,41 @@ static int task_numa_find_cpu(struct task_struct *p, int nid) > > * migrate to its preferred node due to load imbalances. > > */ > > balanced = (dst_eff_load <= src_eff_load); > > - if (!balanced) > > - continue; > > + if (!balanced) { > > + struct rq *rq = cpu_rq(cpu); > > + unsigned long src_faults, dst_faults; > > + > > + /* Do not move tasks off their preferred node */ > > + if (rq->curr->numa_preferred_nid == nid) > > + continue; > > + > > + /* Do not attempt an illegal migration */ > > + if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(rq->curr))) > > + continue; > > + > > + /* > > + * Do not impair locality for the swap candidate. > > + * Destination for the swap candidate is the source cpu > > + */ > > + if (rq->curr->numa_faults) { > > + src_faults = rq->curr->numa_faults[task_faults_idx(nid, 1)]; > > + dst_faults = rq->curr->numa_faults[task_faults_idx(src_cpu_node, 1)]; > > + if (src_faults > dst_faults) > > + continue; > > + } > > + > > + /* > > + * The destination is overloaded but running a task > > + * that is not running on its preferred node. Consider > > + * swapping the CPU tasks are running on. > > + */ > > + swap_candidate = rq->curr; > > + } > > > > if (dst_load < min_load) { > > min_load = dst_load; > > dst_cpu = cpu; > > + *swap_p = swap_candidate; > > Are we some times passing a wrong candidate? > Lets say the first cpu balanced is false and we set the swap_candidate, > but find the second cpu(/or later cpus) to be idle or has lesser effective load, then we > could be sending the task that is running on the first cpu as the swap > candidate.
Then at the second or later CPU swap_candidate == NULL so swap_p is cleared too.
-- Mel Gorman SUSE Labs
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