Messages in this thread | | | Date | Wed, 6 May 2015 19:00:38 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] numa,sched: only consider less busy nodes as numa balancing destination |
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On Wed, May 06, 2015 at 11:41:28AM -0400, Rik van Riel wrote:
> Peter, Mel, I think it may be time to stop waiting for the impedance > mismatch between the load balancer and NUMA balancing to be resolved, > and try to just avoid the issue in the NUMA balancing code...
That's a wee bit unfair since we 'all' decided to let the numa thing rest for a while. So obviously that issue didn't get resolved.
> kernel/sched/fair.c | 30 ++++++++++++++++++++++++++++-- > 1 file changed, 28 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index ffeaa4105e48..480e6a35ab35 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1409,6 +1409,30 @@ static void task_numa_find_cpu(struct task_numa_env *env, > } > } > > +/* Only move tasks to a NUMA node less busy than the current node. */ > +static bool numa_has_capacity(struct task_numa_env *env) > +{ > + struct numa_stats *src = &env->src_stats; > + struct numa_stats *dst = &env->dst_stats; > + > + if (src->has_free_capacity && !dst->has_free_capacity) > + return false; > + > + /* > + * Only consider a task move if the source has a higher destination > + * than the destination, corrected for CPU capacity on each node. > + * > + * src->load dst->load > + * --------------------- vs --------------------- > + * src->compute_capacity dst->compute_capacity > + */ > + if (src->load * dst->compute_capacity > > + dst->load * src->compute_capacity) > + return true; > + > + return false; > +} > + > static int task_numa_migrate(struct task_struct *p) > { > struct task_numa_env env = { > @@ -1463,7 +1487,8 @@ static int task_numa_migrate(struct task_struct *p) > update_numa_stats(&env.dst_stats, env.dst_nid); > > /* Try to find a spot on the preferred nid. */ > - task_numa_find_cpu(&env, taskimp, groupimp); > + if (numa_has_capacity(&env)) > + task_numa_find_cpu(&env, taskimp, groupimp); > > /* > * Look at other nodes in these cases: > @@ -1494,7 +1519,8 @@ static int task_numa_migrate(struct task_struct *p) > env.dist = dist; > env.dst_nid = nid; > update_numa_stats(&env.dst_stats, env.dst_nid); > - task_numa_find_cpu(&env, taskimp, groupimp); > + if (numa_has_capacity(&env)) > + task_numa_find_cpu(&env, taskimp, groupimp); > } > }
Does this not 'duplicate' the logic that we tried for with task_numa_compare():balance section? That is where we try to avoid making a decision that the regular load-balancer will dislike and undo.
Alternatively; you can view that as a cpu guard and the proposed as a node guard, in which case, should it not live inside task_numa_find_cpu()? Instead of guarding all call sites.
In any case, should we mix a bit of imbalance_pct in there?
/me goes ponder this a bit further..
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