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sched/fair: Simplify asym_packing logic for SMT cores

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Callers of asym_smt_can_pull_tasks() check the idle state of the
destination CPU and its SMT siblings, if any. No extra checks are needed
in such function.

Since SMT cores divide capacity among its siblings, priorities only really
make sense if only one sibling is active. This is true for SMT2, SMT4,
SMT8, etc. Do not use asym_packing load balance for this case. Instead,
let find_busiest_group() handle imbalances.

When balancing non-SMT cores or at higher scheduling domains (e.g.,
between MC scheduling groups), continue using priorities.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Len Brown <len.brown@intel.com>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Link: https://lore.kernel.org/r/20230406203148.19182-4-ricardo.neri-calderon@linux.intel.com
This commit is contained in:
Ricardo Neri 2023-04-06 13:31:39 -07:00 committed by Peter Zijlstra
parent eefefa716c
commit ef7657d4d2
1 changed files with 12 additions and 21 deletions
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33
kernel/sched/fair.c
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@ -9366,12 +9366,9 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
* the SMT siblings of @sg are busy. If only one CPU in @sg is busy, pull tasks * the SMT siblings of @sg are busy. If only one CPU in @sg is busy, pull tasks
* only if @dst_cpu has higher priority. * only if @dst_cpu has higher priority.
* *
* If both @dst_cpu and @sg have SMT siblings, and @sg has exactly one more * When dealing with SMT cores, only use priorities if the SMT core has exactly
* busy CPU than @sds::local, let @dst_cpu pull tasks if it has higher priority. * one busy sibling. find_busiest_group() will handle bigger imbalances in the
* Bigger imbalances in the number of busy CPUs will be dealt with in * number of busy CPUs.
* update_sd_pick_busiest().
*
* If @sg does not have SMT siblings, only pull tasks if @sg has lower priority.
* *
* Return: true if @dst_cpu can pull tasks, false otherwise. * Return: true if @dst_cpu can pull tasks, false otherwise.
*/ */
@ -9380,12 +9377,10 @@ static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds,
struct sched_group *sg) struct sched_group *sg)
{ {
#ifdef CONFIG_SCHED_SMT #ifdef CONFIG_SCHED_SMT
bool local_is_smt, sg_is_smt; bool local_is_smt;
int sg_busy_cpus; int sg_busy_cpus;
local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY; 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; sg_busy_cpus = sgs->group_weight - sgs->idle_cpus;
if (!local_is_smt) { if (!local_is_smt) {
@ -9406,21 +9401,17 @@ static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds,
return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
} }
/* @dst_cpu has SMT siblings. */ /*
* If we are here @dst_cpu has SMT siblings and are also idle.
if (sg_is_smt) { *
int local_busy_cpus = sds->local->group_weight - * CPU priorities does not make sense for SMT cores with more than one
sds->local_stat.idle_cpus; * busy sibling.
int busy_cpus_delta = sg_busy_cpus - local_busy_cpus; */
if (group->flags & SD_SHARE_CPUCAPACITY && sg_busy_cpus != 1)
if (busy_cpus_delta == 1)
return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
return false; return false;
}
/* If we are here @dst_cpu has SMT siblings and are also idle. */
return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
#else #else
/* Always return false so that callers deal with non-SMT cases. */ /* Always return false so that callers deal with non-SMT cases. */
return false; return false;