[PATCH v2 06/23] sched/cache: Track LLC-preferred tasks per runqueue

[Tim Chen <tim.c.chen@linux.intel.com>]

For each runqueue, track the number of tasks with an LLC preference
and how many of them are running on their preferred LLC. This mirrors
nr_numa_running and nr_preferred_running for NUMA balancing, and will
be used by cache-aware load balancing in later patches.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---

Notes:
    v1->v2: Invoke task_of() once and reuse its result afterwards.
            (Peter Zijlstra)
            Remove hacky reset_llc_stats() and introduce sched_llc_active flag
            to properly pair enqueue/dequeue statistics update (Peter Zijlstra, K Prateek Nayak)

 include/linux/sched.h |  2 ++
 init/init_task.c      |  1 +
 kernel/sched/core.c   |  5 ++++
 kernel/sched/fair.c   | 60 ++++++++++++++++++++++++++++++++++++++++---
 kernel/sched/sched.h  |  6 +++++
 5 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1ad46220cd04..466ba8b7398c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1408,6 +1408,8 @@ struct task_struct {
 
 #ifdef CONFIG_SCHED_CACHE
 	struct callback_head		cache_work;
+	/*the p is currently refcounted in a rq's preferred llc stats*/
+	bool				sched_llc_active;
 	int				preferred_llc;
 #endif
 
diff --git a/init/init_task.c b/init/init_task.c
index 44bae72b5b7d..ee78837b0aa2 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -192,6 +192,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 	.numa_faults	= NULL,
 #endif
 #ifdef CONFIG_SCHED_CACHE
+	.sched_llc_active = false,
 	.preferred_llc  = -1,
 #endif
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e8bdf03a4b7f..48626c81ba8e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -531,6 +531,11 @@ void __trace_set_current_state(int state_value)
 }
 EXPORT_SYMBOL(__trace_set_current_state);
 
+int task_llc(const struct task_struct *p)
+{
+	return per_cpu(sd_llc_id, task_cpu(p));
+}
+
 /*
  * Serialization rules:
  *
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 10cec83f65d5..d46a70a9d9fb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1223,6 +1223,43 @@ static int llc_id(int cpu)
 	return llc;
 }
 
+static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
+{
+	int pref_llc;
+
+	if (!sched_cache_enabled())
+		return;
+
+	pref_llc = p->preferred_llc;
+	if (pref_llc < 0)
+		return;
+
+	rq->nr_llc_running++;
+	rq->nr_pref_llc_running += (pref_llc == task_llc(p));
+	p->sched_llc_active = true;
+}
+
+static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
+{
+	int pref_llc;
+
+	/*
+	 * Borrow the uc_se->active from uclamp_rq_inc_id(),
+	 * uclamp_rq_dec_id() to avoid the unbalanced calculation
+	 * of rq statistics.
+	 */
+	if (unlikely(!p->sched_llc_active))
+		return;
+
+	pref_llc = p->preferred_llc;
+	if (pref_llc < 0)
+		return;
+
+	rq->nr_llc_running--;
+	rq->nr_pref_llc_running -= (pref_llc == task_llc(p));
+	p->sched_llc_active = false;
+}
+
 void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
@@ -1294,6 +1331,8 @@ static unsigned long __no_profile fraction_mm_sched(struct rq *rq, struct mm_sch
 	return div64_u64(NICE_0_LOAD * pcpu_sched->runtime, rq->cpu_runtime + 1);
 }
 
+static unsigned int task_running_on_cpu(int cpu, struct task_struct *p);
+
 static inline
 void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 {
@@ -1346,8 +1385,13 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 #endif
 	}
 
-	if (p->preferred_llc != mm_sched_llc)
+	/* task not on rq accounted later in account_entity_enqueue() */
+	if (task_running_on_cpu(rq->cpu, p) &&
+	    p->preferred_llc != mm_sched_llc) {
+		account_llc_dequeue(rq, p);
 		p->preferred_llc = mm_sched_llc;
+		account_llc_enqueue(rq, p);
+	}
 }
 
 static void task_tick_cache(struct rq *rq, struct task_struct *p)
@@ -1475,6 +1519,10 @@ void init_sched_mm(struct task_struct *p) { }
 
 static void task_tick_cache(struct rq *rq, struct task_struct *p) { }
 
+static void account_llc_enqueue(struct rq *rq, struct task_struct *p) {}
+
+static void account_llc_dequeue(struct rq *rq, struct task_struct *p) {}
+
 #endif
 
 /*
@@ -3965,9 +4013,11 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	update_load_add(&cfs_rq->load, se->load.weight);
 	if (entity_is_task(se)) {
+		struct task_struct *p = task_of(se);
 		struct rq *rq = rq_of(cfs_rq);
 
-		account_numa_enqueue(rq, task_of(se));
+		account_numa_enqueue(rq, p);
+		account_llc_enqueue(rq, p);
 		list_add(&se->group_node, &rq->cfs_tasks);
 	}
 	cfs_rq->nr_queued++;
@@ -3978,7 +4028,11 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	update_load_sub(&cfs_rq->load, se->load.weight);
 	if (entity_is_task(se)) {
-		account_numa_dequeue(rq_of(cfs_rq), task_of(se));
+		struct task_struct *p = task_of(se);
+		struct rq *rq = rq_of(cfs_rq);
+
+		account_numa_dequeue(rq, p);
+		account_llc_dequeue(rq, p);
 		list_del_init(&se->group_node);
 	}
 	cfs_rq->nr_queued--;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 728737641847..ee8b70647835 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1126,6 +1126,10 @@ struct rq {
 	unsigned int		nr_preferred_running;
 	unsigned int		numa_migrate_on;
 #endif
+#ifdef CONFIG_SCHED_CACHE
+	unsigned int		nr_pref_llc_running;
+	unsigned int		nr_llc_running;
+#endif
 #ifdef CONFIG_NO_HZ_COMMON
 	unsigned long		last_blocked_load_update_tick;
 	unsigned int		has_blocked_load;
@@ -1980,6 +1984,8 @@ init_numa_balancing(u64 clone_flags, struct task_struct *p)
 
 #endif /* !CONFIG_NUMA_BALANCING */
 
+int task_llc(const struct task_struct *p);
+
 static inline void
 queue_balance_callback(struct rq *rq,
 		       struct balance_callback *head,
-- 
2.32.0