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sched/fair: Consider SMT in ASYM_PACKING load balance

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When deciding to pull tasks in ASYM_PACKING, it is necessary not only to
check for the idle state of the destination CPU, dst_cpu, but also of
its SMT siblings.

If dst_cpu is idle but its SMT siblings are busy, performance suffers
if it pulls tasks from a medium priority CPU that does not have SMT
siblings.

Implement asym_smt_can_pull_tasks() to inspect the state of the SMT
siblings of both dst_cpu and the CPUs in the candidate busiest group.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Len Brown <len.brown@intel.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210911011819.12184-7-ricardo.neri-calderon@linux.intel.com
This commit is contained in:
Ricardo Neri 2021-09-10 18:18:19 -07:00 committed by Peter Zijlstra
parent aafc917a3c
commit 4006a72bdd
1 changed files with 92 additions and 0 deletions
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92
kernel/sched/fair.c
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@ -8571,10 +8571,96 @@ group_type group_classify(unsigned int imbalance_pct,
return group_has_spare;
}
/**
* asym_smt_can_pull_tasks - Check whether the load balancing CPU can pull tasks
* @dst_cpu: Destination CPU of the load balancing
* @sds: Load-balancing data with statistics of the local group
* @sgs: Load-balancing statistics of the candidate busiest group
* @sg: The candidate busiest group
*
* Check the state of the SMT siblings of both @sds::local and @sg and decide
* if @dst_cpu can pull tasks.
*
* If @dst_cpu does not have SMT siblings, it can pull tasks if two or more of
* the SMT siblings of @sg are busy. If only one CPU in @sg is busy, pull tasks
* only if @dst_cpu has higher priority.
*
* If both @dst_cpu and @sg have SMT siblings, and @sg has exactly one more
* busy CPU than @sds::local, let @dst_cpu pull tasks if it has higher priority.
* Bigger imbalances in the number of busy CPUs will be dealt with in
* update_sd_pick_busiest().
*
* If @sg does not have SMT siblings, only pull tasks if all of the SMT siblings
* of @dst_cpu are idle and @sg has lower priority.
*/
static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds,
struct sg_lb_stats *sgs,
struct sched_group *sg)
{
#ifdef CONFIG_SCHED_SMT
bool local_is_smt, sg_is_smt;
int sg_busy_cpus;
local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY;
sg_is_smt = sg->flags & SD_SHARE_CPUCAPACITY;
sg_busy_cpus = sgs->group_weight - sgs->idle_cpus;
if (!local_is_smt) {
/*
* If we are here, @dst_cpu is idle and does not have SMT
* siblings. Pull tasks if candidate group has two or more
* busy CPUs.
*/
if (sg_busy_cpus >= 2) /* implies sg_is_smt */
return true;
/*
* @dst_cpu does not have SMT siblings. @sg may have SMT
* siblings and only one is busy. In such case, @dst_cpu
* can help if it has higher priority and is idle (i.e.,
* it has no running tasks).
*/
return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
}
/* @dst_cpu has SMT siblings. */
if (sg_is_smt) {
int local_busy_cpus = sds->local->group_weight -
sds->local_stat.idle_cpus;
int busy_cpus_delta = sg_busy_cpus - local_busy_cpus;
if (busy_cpus_delta == 1)
return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
return false;
}
/*
* @sg does not have SMT siblings. Ensure that @sds::local does not end
* up with more than one busy SMT sibling and only pull tasks if there
* are not busy CPUs (i.e., no CPU has running tasks).
*/
if (!sds->local_stat.sum_nr_running)
return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
return false;
#else
/* Always return false so that callers deal with non-SMT cases. */
return false;
#endif
}
static inline bool
sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs,
struct sched_group *group)
{
/* Only do SMT checks if either local or candidate have SMT siblings */
if ((sds->local->flags & SD_SHARE_CPUCAPACITY) ||
(group->flags & SD_SHARE_CPUCAPACITY))
return asym_smt_can_pull_tasks(env->dst_cpu, sds, sgs, group);
return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
}
@ -9580,6 +9666,12 @@ static struct rq *find_busiest_queue(struct lb_env *env,
nr_running == 1)
continue;
/* Make sure we only pull tasks from a CPU of lower priority */
if ((env->sd->flags & SD_ASYM_PACKING) &&
sched_asym_prefer(i, env->dst_cpu) &&
nr_running == 1)
continue;
switch (env->migration_type) {
case migrate_load:
/*