On Thu, Jun 27, 2013 at 06:11:27PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 26, 2013 at 03:38:04PM +0100, Mel Gorman wrote:
> > +/* Returns true if the destination node has incurred more faults */
> > +static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
> > +{
> > + int src_nid, dst_nid;
> > +
> > + if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
> > + return false;
> > +
> > + src_nid = cpu_to_node(env->src_cpu);
> > + dst_nid = cpu_to_node(env->dst_cpu);
> > +
> > + if (src_nid == dst_nid)
> > + return false;
> > +
> > + if (p->numa_migrate_seq < sysctl_numa_balancing_settle_count &&
> > + p->numa_preferred_nid == dst_nid)
> > + return true;
> > +
> > + return false;
> > +}
>
> Also, until I just actually _read_ that function; I assumed it would
> compare p->numa_faults[src_nid] and p->numa_faults[dst_nid]. Because
> even when the dst_nid isn't the preferred nid; it might still have more
> pages than where we currently are.
>
I tested something like this and also tested it when only taking shared
accesses into account but it performed badly in some cases. I've included
the last patch I tested below for reference but dropped it until I figured
out why it performed badly. I guessed it was due to increased bouncing
due to shared faults but didn't prove it.
> Idem with the proposed migrate_degrades_locality().
>
> Something like so I suppose
>
> ---
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3969,6 +3969,7 @@ task_hot(struct task_struct *p, u64 now,
> return delta < (s64)sysctl_sched_migration_cost;
> }
>
> +#ifdef CONFIG_NUMA_BALANCING
> /* Returns true if the destination node has incurred more faults */
> static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
> {
> @@ -3983,13 +3984,50 @@ static bool migrate_improves_locality(st
> if (src_nid == dst_nid)
> return false;
>
> - if (p->numa_migrate_seq < sysctl_numa_balancing_settle_count &&
> - p->numa_preferred_nid == dst_nid)
> + if (p->numa_migrate_seq >= sysctl_numa_balancing_settle_count)
> + return false;
> +
> + if (p->numa_preferred_nid == dst_nid)
> + return true;
> +
> + if (p->numa_faults[src_nid] < p->numa_faults[dst_nid])
> + return true;
> +
> + return false;
> +}
> +
I tested something like this.
> +static vool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
> +{
> + int src_nid, dst_nid;
> +
> + if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
> + return false;
> +
> + src_nid = cpu_to_node(env->src_cpu);
> + dst_nid = cpu_to_node(env->dst_cpu);
> +
> + if (src_nid == dst_nid)
> + return false;
> +
> + if (p->numa_faults[src_nid] > p->numa_faults[dst_nid])
> return true;
>
> return false;
> }
But I had not tried this and it makes sense. I'll test it out and include
it in the next revision if it looks good. Unless you object I'll add
your signed-off because the version of the patch I'm about to test looks
almost identical to this.
>
> +#else
> +
> +static inline bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
> +{
> + return false;
> +}
> +
> +static inline bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
> +{
> + return false;
> +}
> +
> +#endif /* CONFIG_NUMA_BALANCING */
>
> /*
> * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
> @@ -4055,8 +4093,10 @@ int can_migrate_task(struct task_struct
> return 1;
>
> tsk_cache_hot = task_hot(p, rq_clock_task(env->src_rq), env->sd);
> + if (!tsk_cache_hot)
> + tsk_cache_hot = migrate_degrades_locality(p, env);
> if (!tsk_cache_hot ||
> - env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
> + env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
>
> if (tsk_cache_hot) {
> schedstat_inc(env->sd, lb_hot_gained[env->idle]);
>
This is the last patch similar to this idea I tested.
---8<---
sched: Favour moving tasks towards nodes that incurred more faults
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e9bbb70..3379ca4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3980,9 +3980,18 @@ static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)
if (src_nid == dst_nid)
return false;
- if (p->numa_migrate_seq < sysctl_numa_balancing_settle_count &&
- p->numa_preferred_nid == dst_nid)
- return true;
+ if (p->numa_migrate_seq < sysctl_numa_balancing_settle_count) {
+ if (p->numa_preferred_nid == dst_nid)
+ return true;
+
+ /*
+ * Move towards node if there were a higher number of shared
+ * NUMA hinting faults
+ */
+ if (p->numa_faults[task_faults_idx(dst_nid, 0)] >
+ p->numa_faults[task_faults_idx(src_nid, 0)])
+ return true;
+ }
return false;
}
--
Mel Gorman
SUSE Labs
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