sched/cache: Add migrate_llc_task migration type for cache-aware balancing

Introduce a new migration type, migrate_llc_task, to support
cache-aware load balancing.

After identifying the busiest sched_group (having the most tasks
preferring the destination LLC), mark migrations with this type.
During load balancing, each runqueue in the busiest sched_group is
examined, and the runqueue with the highest number of tasks preferring
the destination CPU is selected as the busiest runqueue.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/b9df27c19cc5121ddb2a7d1be7f9d52fec1563dc.1775065312.git.tim.c.chen@linux.intel.com

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ba4ee9aeea6600eaaa0ff7dbbb29025b25a93217..68032efd143b9d3f1dddc66228e8668b5e76a969 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9946,7 +9946,8 @@ enum migration_type {
        migrate_load = 0,
        migrate_util,
        migrate_task,
-       migrate_misfit
+       migrate_misfit,
+       migrate_llc_task
 };
 
 #define LBF_ALL_PINNED 0x01
@@ -10560,6 +10561,10 @@ static int detach_tasks(struct lb_env *env)
 
                        env->imbalance = 0;
                        break;
+
+               case migrate_llc_task:
+                       env->imbalance--;
+                       break;
                }
 
                detach_task(p, env);
@@ -12179,6 +12184,15 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
                return;
        }
 
+#ifdef CONFIG_SCHED_CACHE
+       if (busiest->group_type == group_llc_balance) {
+               /* Move a task that prefer local LLC */
+               env->migration_type = migrate_llc_task;
+               env->imbalance = 1;
+               return;
+       }
+#endif
+
        if (busiest->group_type == group_imbalanced) {
                /*
                 * In the group_imb case we cannot rely on group-wide averages
@@ -12485,7 +12499,10 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,
 {
        struct rq *busiest = NULL, *rq;
        unsigned long busiest_util = 0, busiest_load = 0, busiest_capacity = 1;
+       unsigned int __maybe_unused busiest_pref_llc = 0;
+       struct sched_domain __maybe_unused *sd_tmp;
        unsigned int busiest_nr = 0;
+       int __maybe_unused dst_llc;
        int i;
 
        for_each_cpu_and(i, sched_group_span(group), env->cpus) {
@@ -12613,6 +12630,23 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,
 
                        break;
 
+               case migrate_llc_task:
+#ifdef CONFIG_SCHED_CACHE
+                       sd_tmp = rcu_dereference_all(rq->sd);
+                       dst_llc = llc_id(env->dst_cpu);
+
+                       if (sd_tmp && (unsigned)dst_llc < sd_tmp->llc_max) {
+                               unsigned int this_pref_llc =
+                                       sd_tmp->llc_counts[dst_llc];
+
+                               if (busiest_pref_llc < this_pref_llc) {
+                                       busiest_pref_llc = this_pref_llc;
+                                       busiest = rq;
+                               }
+                       }
+#endif
+                       break;
+
                }
        }
 
@@ -12776,6 +12810,8 @@ static void update_lb_imbalance_stat(struct lb_env *env, struct sched_domain *sd
        case migrate_misfit:
                __schedstat_add(sd->lb_imbalance_misfit[idle], env->imbalance);
                break;
+       case migrate_llc_task:
+               break;
        }
 }