1 files changed, 155 insertions, 80 deletions

diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c
index 1095e878a46f..76a9ac5eb794 100644
--- a/kernel/sched/cpupri.c
+++ b/kernel/sched/cpupri.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  *  kernel/sched/cpupri.c
  *
@@ -10,50 +11,127 @@
  *  This code tracks the priority of each CPU so that global migration
  *  decisions are easy to calculate.  Each CPU can be in a state as follows:
  *
- *                 (INVALID), IDLE, NORMAL, RT1, ... RT99
+ *                 (INVALID), NORMAL, RT1, ... RT99, HIGHER
  *
  *  going from the lowest priority to the highest.  CPUs in the INVALID state
  *  are not eligible for routing.  The system maintains this state with
- *  a 2 dimensional bitmap (the first for priority class, the second for cpus
+ *  a 2 dimensional bitmap (the first for priority class, the second for CPUs
  *  in that class).  Therefore a typical application without affinity
  *  restrictions can find a suitable CPU with O(1) complexity (e.g. two bit
  *  searches).  For tasks with affinity restrictions, the algorithm has a
- *  worst case complexity of O(min(102, nr_domcpus)), though the scenario that
+ *  worst case complexity of O(min(101, nr_domcpus)), though the scenario that
  *  yields the worst case search is fairly contrived.
- *
- *  This program is free software; you can redistribute it and/or
- *  modify it under the terms of the GNU General Public License
- *  as published by the Free Software Foundation; version 2
- *  of the License.
  */
+#include "sched.h"
 
-#include <linux/gfp.h>
-#include <linux/sched.h>
-#include <linux/sched/rt.h>
-#include "cpupri.h"
-
-/* Convert between a 140 based task->prio, and our 102 based cpupri */
+/*
+ * p->rt_priority   p->prio   newpri   cpupri
+ *
+ *				  -1       -1 (CPUPRI_INVALID)
+ *
+ *				  99        0 (CPUPRI_NORMAL)
+ *
+ *		1        98       98        1
+ *	      ...
+ *	       49        50       50       49
+ *	       50        49       49       50
+ *	      ...
+ *	       99         0        0       99
+ *
+ *				 100	  100 (CPUPRI_HIGHER)
+ */
 static int convert_prio(int prio)
 {
 	int cpupri;
 
-	if (prio == CPUPRI_INVALID)
-		cpupri = CPUPRI_INVALID;
-	else if (prio == MAX_PRIO)
-		cpupri = CPUPRI_IDLE;
-	else if (prio >= MAX_RT_PRIO)
-		cpupri = CPUPRI_NORMAL;
-	else
-		cpupri = MAX_RT_PRIO - prio + 1;
+	switch (prio) {
+	case CPUPRI_INVALID:
+		cpupri = CPUPRI_INVALID;	/* -1 */
+		break;
+
+	case 0 ... 98:
+		cpupri = MAX_RT_PRIO-1 - prio;	/* 1 ... 99 */
+		break;
+
+	case MAX_RT_PRIO-1:
+		cpupri = CPUPRI_NORMAL;		/*  0 */
+		break;
+
+	case MAX_RT_PRIO:
+		cpupri = CPUPRI_HIGHER;		/* 100 */
+		break;
+	}
 
 	return cpupri;
 }
 
+static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p,
+				struct cpumask *lowest_mask, int idx)
+{
+	struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
+	int skip = 0;
+
+	if (!atomic_read(&(vec)->count))
+		skip = 1;
+	/*
+	 * When looking at the vector, we need to read the counter,
+	 * do a memory barrier, then read the mask.
+	 *
+	 * Note: This is still all racy, but we can deal with it.
+	 *  Ideally, we only want to look at masks that are set.
+	 *
+	 *  If a mask is not set, then the only thing wrong is that we
+	 *  did a little more work than necessary.
+	 *
+	 *  If we read a zero count but the mask is set, because of the
+	 *  memory barriers, that can only happen when the highest prio
+	 *  task for a run queue has left the run queue, in which case,
+	 *  it will be followed by a pull. If the task we are processing
+	 *  fails to find a proper place to go, that pull request will
+	 *  pull this task if the run queue is running at a lower
+	 *  priority.
+	 */
+	smp_rmb();
+
+	/* Need to do the rmb for every iteration */
+	if (skip)
+		return 0;
+
+	if (cpumask_any_and(&p->cpus_mask, vec->mask) >= nr_cpu_ids)
+		return 0;
+
+	if (lowest_mask) {
+		cpumask_and(lowest_mask, &p->cpus_mask, vec->mask);
+		cpumask_and(lowest_mask, lowest_mask, cpu_active_mask);
+
+		/*
+		 * We have to ensure that we have at least one bit
+		 * still set in the array, since the map could have
+		 * been concurrently emptied between the first and
+		 * second reads of vec->mask.  If we hit this
+		 * condition, simply act as though we never hit this
+		 * priority level and continue on.
+		 */
+		if (cpumask_empty(lowest_mask))
+			return 0;
+	}
+
+	return 1;
+}
+
+int cpupri_find(struct cpupri *cp, struct task_struct *p,
+		struct cpumask *lowest_mask)
+{
+	return cpupri_find_fitness(cp, p, lowest_mask, NULL);
+}
+
 /**
- * cpupri_find - find the best (lowest-pri) CPU in the system
+ * cpupri_find_fitness - find the best (lowest-pri) CPU in the system
  * @cp: The cpupri context
  * @p: The task
  * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
+ * @fitness_fn: A pointer to a function to do custom checks whether the CPU
+ *              fits a specific criteria so that we only return those CPUs.
  *
  * Note: This function returns the recommended CPUs as calculated during the
  * current invocation.  By the time the call returns, the CPUs may have in
@@ -62,76 +140,69 @@ static int convert_prio(int prio)
  * any discrepancies created by racing against the uncertainty of the current
  * priority configuration.
  *
- * Returns: (int)bool - CPUs were found
+ * Return: (int)bool - CPUs were found
  */
-int cpupri_find(struct cpupri *cp, struct task_struct *p,
-		struct cpumask *lowest_mask)
+int cpupri_find_fitness(struct cpupri *cp, struct task_struct *p,
+		struct cpumask *lowest_mask,
+		bool (*fitness_fn)(struct task_struct *p, int cpu))
 {
-	int idx = 0;
 	int task_pri = convert_prio(p->prio);
+	int idx, cpu;
 
-	if (task_pri >= MAX_RT_PRIO)
-		return 0;
+	WARN_ON_ONCE(task_pri >= CPUPRI_NR_PRIORITIES);
 
 	for (idx = 0; idx < task_pri; idx++) {
-		struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
-		int skip = 0;
-
-		if (!atomic_read(&(vec)->count))
-			skip = 1;
-		/*
-		 * When looking at the vector, we need to read the counter,
-		 * do a memory barrier, then read the mask.
-		 *
-		 * Note: This is still all racey, but we can deal with it.
-		 *  Ideally, we only want to look at masks that are set.
-		 *
-		 *  If a mask is not set, then the only thing wrong is that we
-		 *  did a little more work than necessary.
-		 *
-		 *  If we read a zero count but the mask is set, because of the
-		 *  memory barriers, that can only happen when the highest prio
-		 *  task for a run queue has left the run queue, in which case,
-		 *  it will be followed by a pull. If the task we are processing
-		 *  fails to find a proper place to go, that pull request will
-		 *  pull this task if the run queue is running at a lower
-		 *  priority.
-		 */
-		smp_rmb();
 
-		/* Need to do the rmb for every iteration */
-		if (skip)
+		if (!__cpupri_find(cp, p, lowest_mask, idx))
 			continue;
 
-		if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
-			continue;
+		if (!lowest_mask || !fitness_fn)
+			return 1;
 
-		if (lowest_mask) {
-			cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
-
-			/*
-			 * We have to ensure that we have at least one bit
-			 * still set in the array, since the map could have
-			 * been concurrently emptied between the first and
-			 * second reads of vec->mask.  If we hit this
-			 * condition, simply act as though we never hit this
-			 * priority level and continue on.
-			 */
-			if (cpumask_any(lowest_mask) >= nr_cpu_ids)
-				continue;
+		/* Ensure the capacity of the CPUs fit the task */
+		for_each_cpu(cpu, lowest_mask) {
+			if (!fitness_fn(p, cpu))
+				cpumask_clear_cpu(cpu, lowest_mask);
 		}
 
+		/*
+		 * If no CPU at the current priority can fit the task
+		 * continue looking
+		 */
+		if (cpumask_empty(lowest_mask))
+			continue;
+
 		return 1;
 	}
 
+	/*
+	 * If we failed to find a fitting lowest_mask, kick off a new search
+	 * but without taking into account any fitness criteria this time.
+	 *
+	 * This rule favours honouring priority over fitting the task in the
+	 * correct CPU (Capacity Awareness being the only user now).
+	 * The idea is that if a higher priority task can run, then it should
+	 * run even if this ends up being on unfitting CPU.
+	 *
+	 * The cost of this trade-off is not entirely clear and will probably
+	 * be good for some workloads and bad for others.
+	 *
+	 * The main idea here is that if some CPUs were over-committed, we try
+	 * to spread which is what the scheduler traditionally did. Sys admins
+	 * must do proper RT planning to avoid overloading the system if they
+	 * really care.
+	 */
+	if (fitness_fn)
+		return cpupri_find(cp, p, lowest_mask);
+
 	return 0;
 }
 
 /**
- * cpupri_set - update the cpu priority setting
+ * cpupri_set - update the CPU priority setting
  * @cp: The cpupri context
- * @cpu: The target cpu
- * @newpri: The priority (INVALID-RT99) to assign to this CPU
+ * @cpu: The target CPU
+ * @newpri: The priority (INVALID,NORMAL,RT1-RT99,HIGHER) to assign to this CPU
  *
  * Note: Assumes cpu_rq(cpu)->lock is locked
  *
@@ -151,7 +222,7 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 		return;
 
 	/*
-	 * If the cpu was currently mapped to a different value, we
+	 * If the CPU was currently mapped to a different value, we
 	 * need to map it to the new value then remove the old value.
 	 * Note, we must add the new value first, otherwise we risk the
 	 * cpu being missed by the priority loop in cpupri_find.
@@ -165,7 +236,7 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 		 * do a write memory barrier, and then update the count, to
 		 * make sure the vector is visible when count is set.
 		 */
-		smp_mb__before_atomic_inc();
+		smp_mb__before_atomic();
 		atomic_inc(&(vec)->count);
 		do_mb = 1;
 	}
@@ -185,14 +256,14 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 		 * the new priority vec.
 		 */
 		if (do_mb)
-			smp_mb__after_atomic_inc();
+			smp_mb__after_atomic();
 
 		/*
 		 * When removing from the vector, we decrement the counter first
 		 * do a memory barrier and then clear the mask.
 		 */
 		atomic_dec(&(vec)->count);
-		smp_mb__after_atomic_inc();
+		smp_mb__after_atomic();
 		cpumask_clear_cpu(cpu, vec->mask);
 	}
 
@@ -203,14 +274,12 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
  * cpupri_init - initialize the cpupri structure
  * @cp: The cpupri context
  *
- * Returns: -ENOMEM if memory fails.
+ * Return: -ENOMEM on memory allocation failure.
  */
 int cpupri_init(struct cpupri *cp)
 {
 	int i;
 
-	memset(cp, 0, sizeof(*cp));
-
 	for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
 		struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 
@@ -219,8 +288,13 @@ int cpupri_init(struct cpupri *cp)
 			goto cleanup;
 	}
 
+	cp->cpu_to_pri = kcalloc(nr_cpu_ids, sizeof(int), GFP_KERNEL);
+	if (!cp->cpu_to_pri)
+		goto cleanup;
+
 	for_each_possible_cpu(i)
 		cp->cpu_to_pri[i] = CPUPRI_INVALID;
+
 	return 0;
 
 cleanup:
@@ -237,6 +311,7 @@ void cpupri_cleanup(struct cpupri *cp)
 {
 	int i;
 
+	kfree(cp->cpu_to_pri);
 	for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
 		free_cpumask_var(cp->pri_to_cpu[i].mask);
 }