[RFC PATCH 16/23] thermal: intel: hfi: Define a default classification for unclassified tasks

[Ricardo Neri]

Tasks may be unclassified if they have been recently created, spend most
of its lifetime sleeping, or hardware has not provided a classification.

Most tasks will be eventually classified as 0. This class corresponds to
the capabilities in the legacy, classless, Hardware Feedback Interface
table.

Class 0 is a reasonable choice until hardware provides an actual
classification. Meanwhile, the scheduler will place tasks of higher-
performance classes on higher-performance CPUs.

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>
---
 drivers/thermal/intel/intel_hfi.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
index 1b6072c828ff..967899d2c01f 100644
--- a/drivers/thermal/intel/intel_hfi.c
+++ b/drivers/thermal/intel/intel_hfi.c
@@ -184,6 +184,20 @@ static struct workqueue_struct *hfi_updates_wq;
 #define HFI_MAX_THERM_NOTIFY_COUNT	16
 
 #ifdef CONFIG_INTEL_THREAD_DIRECTOR
+
+/*
+ * Tasks may be unclassified if they have been recently created, spend most
+ * of its lifetime sleeping, or hardware has not provided a classification.
+ *
+ * Most tasks will be classified as 0 eventually. Meanwhile, the scheduler
+ * will place tasks of higher per-class performance on higher-performance
+ * CPUs.
+ *
+ * Class 0 is a reasonable choice. It matches the performance capability
+ * of the legacy, classless, Hardware Feedback Interface table.
+ */
+#define UNCLASSIFIED_TASK_DEFAULT 0
+
 int intel_hfi_has_task_classes(void)
 {
 	return cpu_feature_enabled(X86_FEATURE_ITD);
@@ -222,14 +236,14 @@ int intel_hfi_get_task_class_score(int class, int cpu)
 	struct hfi_cpu_info *info = &per_cpu(hfi_cpu_info, cpu);
 	struct hfi_instance *instance;
 	struct hfi_cpu_data caps;
+	int cap, _class = class;
 	unsigned long flags;
-	int cap;
 
 	if (cpu < 0 || cpu >= nr_cpu_ids)
 		return -EINVAL;
 
 	if (class == TASK_CLASS_UNCLASSIFIED)
-		return -EINVAL;
+		_class = UNCLASSIFIED_TASK_DEFAULT;
 
 	if (class >= (int)hfi_features.nr_classes)
 		return -EINVAL;
@@ -239,7 +253,7 @@ int intel_hfi_get_task_class_score(int class, int cpu)
 		return -ENOENT;
 
 	raw_spin_lock_irqsave(&instance->table_lock, flags);
-	get_one_hfi_cap(instance, info->index, &caps, class);
+	get_one_hfi_cap(instance, info->index, &caps, _class);
 	cap = caps.perf_cap;
 	raw_spin_unlock_irqrestore(&instance->table_lock, flags);
 
-- 
2.25.1