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sched/fair: Improve consistency of allowed NUMA balance calculations

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There are inconsistencies when determining if a NUMA imbalance is allowed
that should be corrected.

o allow_numa_imbalance changes types and is not always examining
  the destination group so both the type should be corrected as
  well as the naming.
o find_idlest_group uses the sched_domain's weight instead of the
  group weight which is different to find_busiest_group
o find_busiest_group uses the source group instead of the destination
  which is different to task_numa_find_cpu
o Both find_idlest_group and find_busiest_group should account
  for the number of running tasks if a move was allowed to be
  consistent with task_numa_find_cpu

Fixes: 7d2b5dd0bc ("sched/numa: Allow a floating imbalance between NUMA nodes")
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/r/20220208094334.16379-2-mgorman@techsingularity.net
This commit is contained in:
Mel Gorman 2022-02-08 09:43:33 +00:00 committed by Peter Zijlstra
parent 889c5d60fb
commit 2cfb7a1b03
1 changed files with 10 additions and 8 deletions
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18
kernel/sched/fair.c
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@ -9005,9 +9005,10 @@ static bool update_pick_idlest(struct sched_group *idlest,
* This is an approximation as the number of running tasks may not be
* related to the number of busy CPUs due to sched_setaffinity.
*/
static inline bool allow_numa_imbalance(int dst_running, int dst_weight)
static inline bool
allow_numa_imbalance(unsigned int running, unsigned int weight)
{
return (dst_running < (dst_weight >> 2));
return (running < (weight >> 2));
}
/*
@ -9141,12 +9142,13 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
return idlest;
#endif
/*
* Otherwise, keep the task on this node to stay close
* its wakeup source and improve locality. If there is
* a real need of migration, periodic load balance will
* take care of it.
* Otherwise, keep the task close to the wakeup source
* and improve locality if the number of running tasks
* would remain below threshold where an imbalance is
* allowed. If there is a real need of migration,
* periodic load balance will take care of it.
*/
if (allow_numa_imbalance(local_sgs.sum_nr_running, sd->span_weight))
if (allow_numa_imbalance(local_sgs.sum_nr_running + 1, local_sgs.group_weight))
return NULL;
}
@ -9352,7 +9354,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
/* Consider allowing a small imbalance between NUMA groups */
if (env->sd->flags & SD_NUMA) {
env->imbalance = adjust_numa_imbalance(env->imbalance,
busiest->sum_nr_running, busiest->group_weight);
local->sum_nr_running + 1, local->group_weight);
}
return;