[RFC PATCH 02/23] sched: Add interfaces for classes of tasks

[Ricardo Neri]

Add the interfaces that architectures shall implement to convey needed data
to support classes of tasks.

arch_update_task_class() updates the classification of the current task as
given by dedicated hardware resources.

arch_get_task_class_score() provides a performance score for a given class
of task when placed on a specific CPU relative to other CPUs. Higher scores
indicate higher performance.

The number of classes and the score of each class of task is determined
by hardware.

Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 kernel/sched/sched.h    | 64 +++++++++++++++++++++++++++++++++++++++++
 kernel/sched/topology.c |  8 ++++++
 2 files changed, 72 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e26688d387ae..719bdba660e2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2510,6 +2510,70 @@ void arch_scale_freq_tick(void)
 }
 #endif
 
+#ifdef CONFIG_SCHED_TASK_CLASSES
+DECLARE_STATIC_KEY_FALSE(sched_task_classes);
+
+static inline bool sched_task_classes_enabled(void)
+{
+	return static_branch_unlikely(&sched_task_classes);
+}
+
+#ifndef arch_has_task_classes
+/**
+ * arch_has_task_classes() - Check whether hardware supports classes of tasks
+ *
+ * Returns: true of classes of tasks are supported.
+ */
+static __always_inline
+bool arch_has_task_classes(void)
+{
+	return false;
+}
+#endif
+
+#ifndef arch_update_task_class
+/**
+ * arch_update_task_class() - Update the classification of the current task
+ * @curr:		The current task
+ * @smt_siblings_idle:	True if all of the SMT siblings of the CPU of @curr
+ *			are idle.
+ *
+ * Request that the classification of @curr is updated. On certain CPUs, the
+ * classification is only reliable if all of the SMT siblings of the CPU of
+ * @curr are idle.
+ *
+ * Returns: none
+ */
+static __always_inline
+void arch_update_task_class(struct task_struct *curr, bool smt_siblings_idle)
+{
+}
+#endif
+
+#ifndef arch_get_task_class_score
+/**
+ * arch_get_task_class_score() - Get the priority of a class
+ * @class:	A classification value
+ * @cpu:	A CPU number
+ *
+ * Returns the performance score of a class of tasks when running on @cpu.
+ * Error when either @class or @cpu are invalid.
+ */
+static __always_inline
+int arch_get_task_class_score(int class, int cpu)
+{
+	return 1;
+}
+#endif
+#else /* CONFIG_SCHED_TASK_CLASSES */
+
+#define arch_get_task_class_score(class, cpu) (-EINVAL)
+#define arch_update_task_class(curr, smt_siblings_idle)
+
+static inline bool sched_task_classes_enabled(void) { return false; }
+
+#endif /* CONFIG_SCHED_TASK_CLASSES */
+
 #ifndef arch_scale_freq_capacity
 /**
  * arch_scale_freq_capacity - get the frequency scale factor of a given CPU.
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8739c2a5a54e..8d886dbe6318 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -669,6 +669,9 @@ DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
 DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
+#ifdef CONFIG_SCHED_TASK_CLASSES
+DEFINE_STATIC_KEY_FALSE(sched_task_classes);
+#endif
 
 static void update_top_cache_domain(int cpu)
 {
@@ -2384,6 +2387,11 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 	if (has_asym)
 		static_branch_inc_cpuslocked(&sched_asym_cpucapacity);
 
+#ifdef CONFIG_SCHED_TASK_CLASSES
+	if (arch_has_task_classes())
+		static_branch_enable_cpuslocked(&sched_task_classes);
+#endif
+
 	if (rq && sched_debug_verbose) {
 		pr_info("root domain span: %*pbl (max cpu_capacity = %lu)\n",
 			cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
-- 
2.25.1