linux-kernel - [RFC PATCH v4 13/28] sched: Tag the sched group as llc

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Message-Id: <c111a2b0837ba1616a558f5797d63294e062c33d.1754712565.git.tim.c.chen@linux.intel.com>
Date: Sat,  9 Aug 2025 13:05:44 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Libo Chen <libo.chen@...cle.com>,
	Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
	Hillf Danton <hdanton@...a.com>,
	Shrikanth Hegde <sshegde@...ux.ibm.com>,
	Jianyong Wu <jianyong.wu@...look.com>,
	Yangyu Chen <cyy@...self.name>,
	Tingyin Duan <tingyin.duan@...il.com>,
	Vern Hao <vernhao@...cent.com>,
	Len Brown <len.brown@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Aubrey Li <aubrey.li@...el.com>,
	Zhao Liu <zhao1.liu@...el.com>,
	Chen Yu <yu.chen.surf@...il.com>,
	Chen Yu <yu.c.chen@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v4 13/28] sched: Tag the sched group as llc_balance if it has tasks prefer other LLC

From: Tim Chen <tim.c.chen@...ux.intel.com>

During load balancing between LLCs, check whether there are tasks
preferring the destination LLC. If so, balance those tasks to the
destination LLC first.

Tag the sched_group that has tasks preferring to run on other LLCs
(non-local) with the group_llc_balance flag. This way, the load
balancer will later attempt to pull/push these tasks to their
preferred LLCs.

Co-developed-by: Chen Yu <yu.c.chen@...el.com>
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---
 kernel/sched/fair.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f1697658c3b8..30ebc7d1b999 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10491,6 +10491,7 @@ struct sg_lb_stats {
 	enum group_type group_type;
 	unsigned int group_asym_packing;	/* Tasks should be moved to preferred CPU */
 	unsigned int group_smt_balance;		/* Task on busy SMT be moved */
+	unsigned int group_llc_balance;		/* Tasks should be moved to preferred LLC */
 	unsigned long group_misfit_task_load;	/* A CPU has a task too big for its capacity */
 #ifdef CONFIG_NUMA_BALANCING
 	unsigned int nr_numa_running;
@@ -10855,6 +10856,43 @@ static inline bool smt_balance(struct lb_env *env, struct sg_lb_stats *sgs,
 	return false;
 }
 
+/*
+ * Do LLC balance on sched group that contains LLC, and have tasks preferring
+ * to run on LLC in idle dst_cpu.
+ */
+#ifdef CONFIG_SCHED_CACHE
+static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
+			       struct sched_group *group)
+{
+	struct sched_domain *child = env->sd->child;
+	int llc;
+
+	if (!sched_feat(SCHED_CACHE))
+		return false;
+
+	if (env->sd->flags & SD_SHARE_LLC)
+		return false;
+
+	/* only care about task migration among LLCs */
+	if (child && !(child->flags & SD_SHARE_LLC))
+		return false;
+
+	llc = llc_idx(env->dst_cpu);
+	if (sgs->nr_pref_llc[llc] > 0 &&
+	    _get_migrate_hint(env->src_cpu, env->dst_cpu,
+			      0, true) == mig_allow)
+		return true;
+
+	return false;
+}
+#else
+static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
+			       struct sched_group *group)
+{
+	return false;
+}
+#endif
+
 static inline long sibling_imbalance(struct lb_env *env,
 				    struct sd_lb_stats *sds,
 				    struct sg_lb_stats *busiest,
@@ -11037,6 +11075,11 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 	sgs->group_type = group_classify(env->sd->imbalance_pct, group, sgs);
 
 	update_sg_if_llc(env, sgs, group);
+
+	/* Check for tasks in this group can be moved to their preferred LLC */
+	if (!local_group && llc_balance(env, sgs, group))
+		sgs->group_llc_balance = 1;
+
 	/* Computing avg_load makes sense only when group is overloaded */
 	if (sgs->group_type == group_overloaded)
 		sgs->avg_load = (sgs->group_load * SCHED_CAPACITY_SCALE) /
-- 
2.25.1