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Date: Wed, 10 May 2023 13:49:12 -0000
From: "tip-bot2 for Ricardo Neri" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Zhang Rui <rui.zhang@...el.com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/fair: Do not even the number of busy CPUs via
asym_packing
The following commit has been merged into the sched/core branch of tip:
Commit-ID: c9ca07886aaa40225a29e5c1e46ac31d2e14f53a
Gitweb: https://git.kernel.org/tip/c9ca07886aaa40225a29e5c1e46ac31d2e14f53a
Author: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
AuthorDate: Thu, 06 Apr 2023 13:31:43 -07:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 08 May 2023 10:58:36 +02:00
sched/fair: Do not even the number of busy CPUs via asym_packing
Now that find_busiest_group() triggers load balancing between a fully_
busy SMT2 core and an idle non-SMT core, it is no longer needed to force
balancing via asym_packing. Use asym_packing only as intended: when there
is high-priority CPU that is idle.
After this change, the same logic apply to SMT and non-SMT local groups.
It makes less sense having a separate function to deal specifically with
SMT. Fold the logic in asym_smt_can_pull_tasks() into sched_asym().
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Zhang Rui <rui.zhang@...el.com>
Link: https://lore.kernel.org/r/20230406203148.19182-8-ricardo.neri-calderon@linux.intel.com
---
kernel/sched/fair.c | 86 ++++++++++----------------------------------
1 file changed, 21 insertions(+), 65 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3bb8934..48b6f0c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9350,74 +9350,26 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
}
/**
- * asym_smt_can_pull_tasks - Check whether the load balancing CPU can pull tasks
- * @dst_cpu: Destination CPU of the load balancing
+ * sched_asym - Check if the destination CPU can do asym_packing load balance
+ * @env: The load balancing environment
* @sds: Load-balancing data with statistics of the local group
* @sgs: Load-balancing statistics of the candidate busiest group
- * @sg: The candidate busiest group
+ * @group: 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.
+ * @env::dst_cpu can do asym_packing if it has higher priority than the
+ * preferred CPU of @group.
*
- * This function must be called only if all the SMT siblings of @dst_cpu are
- * idle, if any.
+ * SMT is a special case. If we are balancing load between cores, @env::dst_cpu
+ * can do asym_packing balance only if all its SMT siblings are idle. Also, it
+ * can only do it if @group is an SMT group and has exactly on busy CPU. Larger
+ * imbalances in the number of CPUS are dealt with in find_busiest_group().
*
- * 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 we are balancing load within an SMT core, or at DIE domain level, always
+ * proceed.
*
- * When dealing with SMT cores, only use priorities if the SMT core has exactly
- * one busy sibling. find_busiest_group() will handle bigger imbalances in the
- * number of busy CPUs.
- *
- * Return: true if @dst_cpu can pull tasks, false otherwise.
+ * Return: true if @env::dst_cpu can do with asym_packing load balance. False
+ * otherwise.
*/
-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;
- int sg_busy_cpus;
-
- local_is_smt = sds->local->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);
- }
-
- /*
- * If we are here @dst_cpu has SMT siblings and are also idle.
- *
- * CPU priorities does not make sense for SMT cores with more than one
- * busy sibling.
- */
- if (group->flags & SD_SHARE_CPUCAPACITY && sg_busy_cpus != 1)
- return false;
-
- return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
-
-#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)
@@ -9426,10 +9378,14 @@ sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs
if (!sched_use_asym_prio(env->sd, env->dst_cpu))
return false;
- /* 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);
+ /*
+ * CPU priorities does not make sense for SMT cores with more than one
+ * busy sibling.
+ */
+ if (group->flags & SD_SHARE_CPUCAPACITY) {
+ if (sgs->group_weight - sgs->idle_cpus != 1)
+ return false;
+ }
return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
}
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