[RFC PATCH v4 02/28] sched: Several fixes for cache aware scheduling

[Chen Yu <yu.c.chen@intel.com>]

1. Fix compile error on percpu allocation.
2. Enqueue to the target CPU rather than the current CPU.
3. NULL LLC sched domain check(Libo Chen).
4. Introduce sched feature SCHED_CACHE to control cache aware scheduling
5. Fix unsigned occupancy initialization to -1.
6. If there is only 1 thread in the process, no need to enable cache
   awareness
7. Add __maybe_unused to __migrate_degrades_locality() to
   avoid compile warnings.
8. Do not enable gcov coverage for task_cache_work() and
   fraction_mm_sched() to avoid softlockup by gcov.
9. Make CONFIG_SCHED_CACHE depending on CONFIG_SMP to
   avoid compile error on non-SMP system like microblaze
   architecture.
10. Do not enable account cache aware statistics in
    account_mm_sched() for non-normal tasks, as it could
    be invoked by RT tasks.(Shrikanth Hegde)
11. Place cpu_epoch related fields in a dedicated cache line
    to avoid interfering with clock_idle* fields.
    (Shrikanth Hegde)

Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 include/linux/mm_types.h |  4 ++--
 init/Kconfig             |  4 ++++
 kernel/sched/fair.c      | 41 +++++++++++++++++++++++++++-------------
 kernel/sched/features.h  |  1 +
 kernel/sched/sched.h     |  2 +-
 5 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index cf26ad8b41ab..41a598a44361 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1450,11 +1450,11 @@ static inline void mm_set_cpus_allowed(struct mm_struct *mm, const struct cpumas
 #endif /* CONFIG_SCHED_MM_CID */
 
 #ifdef CONFIG_SCHED_CACHE
-extern void mm_init_sched(struct mm_struct *mm, struct mm_sched *pcpu_sched);
+void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *pcpu_sched);
 
 static inline int mm_alloc_sched_noprof(struct mm_struct *mm)
 {
-	struct mm_sched *pcpu_sched = alloc_percpu_noprof(struct mm_sched);
+	struct mm_sched __percpu *pcpu_sched = alloc_percpu_noprof(struct mm_sched);
 	if (!pcpu_sched)
 		return -ENOMEM;
 
diff --git a/init/Kconfig b/init/Kconfig
index 27f4012347f9..4bab39a5254c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -950,6 +950,10 @@ config NUMA_BALANCING
 config SCHED_CACHE
 	bool "Cache aware scheduler"
 	default y
+	depends on SMP
+	help
+	  If set, the scheduler will try to aggregate tasks in the same process to
+	  a single LLC if possible.
 
 config NUMA_BALANCING_DEFAULT_ENABLED
 	bool "Automatically enable NUMA aware memory/task placement"
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e3897cd7696d..e97ab46509e3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1175,7 +1175,7 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
 #define EPOCH_PERIOD	(HZ/100)	/* 10 ms */
 #define EPOCH_OLD	5		/* 50 ms */
 
-void mm_init_sched(struct mm_struct *mm, struct mm_sched *_pcpu_sched)
+void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
 	int i;
@@ -1186,7 +1186,7 @@ void mm_init_sched(struct mm_struct *mm, struct mm_sched *_pcpu_sched)
 
 		pcpu_sched->runtime = 0;
 		pcpu_sched->epoch = epoch = rq->cpu_epoch;
-		pcpu_sched->occ = -1;
+		pcpu_sched->occ = 0;
 	}
 
 	raw_spin_lock_init(&mm->mm_sched_lock);
@@ -1227,7 +1227,7 @@ static inline void __update_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
 	}
 }
 
-static unsigned long fraction_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
+static unsigned long __no_profile fraction_mm_sched(struct rq *rq, struct mm_sched *pcpu_sched)
 {
 	guard(raw_spinlock_irqsave)(&rq->cpu_epoch_lock);
 
@@ -1248,13 +1248,18 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	struct mm_sched *pcpu_sched;
 	unsigned long epoch;
 
+	if (!sched_feat(SCHED_CACHE))
+		return;
+
+	if (p->sched_class != &fair_sched_class)
+		return;
 	/*
 	 * init_task and kthreads don't be having no mm
 	 */
 	if (!mm || !mm->pcpu_sched)
 		return;
 
-	pcpu_sched = this_cpu_ptr(p->mm->pcpu_sched);
+	pcpu_sched = per_cpu_ptr(p->mm->pcpu_sched, cpu_of(rq));
 
 	scoped_guard (raw_spinlock, &rq->cpu_epoch_lock) {
 		__update_mm_sched(rq, pcpu_sched);
@@ -1264,12 +1269,14 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	}
 
 	/*
-	 * If this task hasn't hit task_cache_work() for a while, invalidate
+	 * If this task hasn't hit task_cache_work() for a while, or it
+	 * has only 1 thread, invalidate
 	 * it's preferred state.
 	 */
-	if (epoch - READ_ONCE(mm->mm_sched_epoch) > EPOCH_OLD) {
+	if (epoch - READ_ONCE(mm->mm_sched_epoch) > EPOCH_OLD ||
+	    get_nr_threads(p) <= 1) {
 		mm->mm_sched_cpu = -1;
-		pcpu_sched->occ = -1;
+		pcpu_sched->occ = 0;
 	}
 }
 
@@ -1278,6 +1285,9 @@ static void task_tick_cache(struct rq *rq, struct task_struct *p)
 	struct callback_head *work = &p->cache_work;
 	struct mm_struct *mm = p->mm;
 
+	if (!sched_feat(SCHED_CACHE))
+		return;
+
 	if (!mm || !mm->pcpu_sched)
 		return;
 
@@ -1286,16 +1296,13 @@ static void task_tick_cache(struct rq *rq, struct task_struct *p)
 
 	guard(raw_spinlock)(&mm->mm_sched_lock);
 
-	if (mm->mm_sched_epoch == rq->cpu_epoch)
-		return;
-
 	if (work->next == work) {
 		task_work_add(p, work, TWA_RESUME);
 		WRITE_ONCE(mm->mm_sched_epoch, rq->cpu_epoch);
 	}
 }
 
-static void task_cache_work(struct callback_head *work)
+static void __no_profile task_cache_work(struct callback_head *work)
 {
 	struct task_struct *p = current;
 	struct mm_struct *mm = p->mm;
@@ -1322,6 +1329,9 @@ static void task_cache_work(struct callback_head *work)
 			unsigned long occ, m_occ = 0, a_occ = 0;
 			int m_cpu = -1, nr = 0, i;
 
+			if (!sd)
+				continue;
+
 			for_each_cpu(i, sched_domain_span(sd)) {
 				occ = fraction_mm_sched(cpu_rq(i),
 							per_cpu_ptr(mm->pcpu_sched, i));
@@ -8815,6 +8825,9 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	struct mm_struct *mm = p->mm;
 	int cpu;
 
+	if (!sched_feat(SCHED_CACHE))
+		return prev_cpu;
+
 	if (!mm || p->nr_cpus_allowed == 1)
 		return prev_cpu;
 
@@ -9569,7 +9582,7 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 		return 0;
 
 #ifdef CONFIG_SCHED_CACHE
-	if (p->mm && p->mm->pcpu_sched) {
+	if (sched_feat(SCHED_CACHE) && p->mm && p->mm->pcpu_sched) {
 		/*
 		 * XXX things like Skylake have non-inclusive L3 and might not
 		 * like this L3 centric view. What to do about L2 stickyness ?
@@ -9647,7 +9660,9 @@ static long migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 }
 
 #else
-static long __migrate_degrades_locality(struct task_struct *p, int src_cpu, int dst_cpu, bool idle)
+static __maybe_unused long __migrate_degrades_locality(struct task_struct *p,
+						       int src_cpu, int dst_cpu,
+						       bool idle)
 {
 	return 0;
 }
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 3c12d9f93331..d2af7bfd36bf 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -87,6 +87,7 @@ SCHED_FEAT(TTWU_QUEUE, true)
  */
 SCHED_FEAT(SIS_UTIL, true)
 
+SCHED_FEAT(SCHED_CACHE, true)
 /*
  * Issue a WARN when we do multiple update_rq_clock() calls
  * in a single rq->lock section. Default disabled because the
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 839463027ab0..f4ab45ecca86 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1174,7 +1174,7 @@ struct rq {
 	u64			clock_idle_copy;
 #endif
 #ifdef CONFIG_SCHED_CACHE
-	raw_spinlock_t		cpu_epoch_lock;
+	raw_spinlock_t		cpu_epoch_lock ____cacheline_aligned;
 	u64			cpu_runtime;
 	unsigned long		cpu_epoch;
 	unsigned long		cpu_epoch_next;
-- 
2.25.1