arm64: Cpu invariant scheduler load-tracking support

Counterpart of the arm bits (slightly different implementation
due to different parsing of the dtb).

Signed-off-by: Juri Lelli <juri.lelli@arm.com>

1 files changed, 20 insertions, 40 deletions

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 59a48b8b9b44..1bbf17301f10 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -197,9 +197,7 @@ struct cpu_efficiency {
  * Table of relative efficiency of each processors
  * The efficiency value must fit in 20bit and the final
  * cpu_scale value must be in the range
- *   0 < cpu_scale < 3*SCHED_CAPACITY_SCALE/2
- * in order to return at most 1 when DIV_ROUND_CLOSEST
- * is used to compute the capacity of a CPU.
+ *   0 < cpu_scale < SCHED_CAPACITY_SCALE.
  * Processors that are not defined in the table,
  * use the default SCHED_CAPACITY_SCALE value for cpu_scale.
  */
@@ -212,15 +210,11 @@ static const struct cpu_efficiency table_efficiency[] = {
 static unsigned long *__cpu_capacity;
 #define cpu_capacity(cpu)	__cpu_capacity[cpu]
 
-static unsigned long middle_capacity = 1;
+static unsigned long max_cpu_perf;
 
 /*
  * Iterate all CPUs' descriptor in DT and compute the efficiency
- * (as per table_efficiency). Also calculate a middle efficiency
- * as close as possible to  (max{eff_i} - min{eff_i}) / 2
- * This is later used to scale the cpu_capacity field such that an
- * 'average' CPU is of middle capacity. Also see the comments near
- * table_efficiency[] and update_cpu_capacity().
+ * (as per table_efficiency). Calculate the max cpu performance too.
  */
 static int __init parse_dt_topology(void)
 {
@@ -269,9 +263,6 @@ static void __init parse_dt_cpu_capacity(void)
 {
 	const struct cpu_efficiency *cpu_eff;
 	struct device_node *cn;
-	unsigned long min_capacity = ULONG_MAX;
-	unsigned long max_capacity = 0;
-	unsigned long capacity = 0;
 	int cpu;
 
 	__cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
@@ -280,6 +271,7 @@ static void __init parse_dt_cpu_capacity(void)
 	for_each_possible_cpu(cpu) {
 		const u32 *rate;
 		int len;
+		unsigned long cpu_perf;
 
 		/* Too early to use cpu->of_node */
 		cn = of_get_cpu_node(cpu, NULL);
@@ -304,47 +296,35 @@ static void __init parse_dt_cpu_capacity(void)
 			continue;
 		}
 
-		capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;
-
-		/* Save min capacity of the system */
-		if (capacity < min_capacity)
-			min_capacity = capacity;
-
-		/* Save max capacity of the system */
-		if (capacity > max_capacity)
-			max_capacity = capacity;
-
-		cpu_capacity(cpu) = capacity;
+		cpu_perf = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;
+		cpu_capacity(cpu) = cpu_perf;
+		max_cpu_perf = max(max_cpu_perf, cpu_perf);
 	}
 
-	/* If min and max capacities are equal we bypass the update of the
-	 * cpu_scale because all CPUs have the same capacity. Otherwise, we
-	 * compute a middle_capacity factor that will ensure that the capacity
-	 * of an 'average' CPU of the system will be as close as possible to
-	 * SCHED_CAPACITY_SCALE, which is the default value, but with the
-	 * constraint explained near table_efficiency[].
-	 */
-	if (min_capacity == max_capacity)
-		return;
-	else if (4 * max_capacity < (3 * (max_capacity + min_capacity)))
-		middle_capacity = (min_capacity + max_capacity)
-				>> (SCHED_CAPACITY_SHIFT+1);
-	else
-		middle_capacity = ((max_capacity / 3)
-				>> (SCHED_CAPACITY_SHIFT-1)) + 1;
+	if (cpu < num_possible_cpus())
+		max_cpu_perf = 0;
 }
 
 /*
  * Look for a customed capacity of a CPU in the cpu_topo_data table during the
  * boot. The update of all CPUs is in O(n^2) for heteregeneous system but the
- * function returns directly for SMP system.
+ * function returns directly for SMP system or if there is no complete set
+ * of cpu efficiency, clock frequency data for each cpu.
  */
 static void update_cpu_capacity(unsigned int cpu)
 {
+	unsigned long capacity;
+
 	if (!cpu_capacity(cpu))
 		return;
 
-	set_capacity_scale(cpu, cpu_capacity(cpu) / middle_capacity);
+	if (!max_cpu_perf)
+		cpu_capacity(cpu) = 0;
+
+	capacity = cpu_capacity(cpu);
+	capacity *= SCHED_CAPACITY_SCALE;
+	capacity /= max_cpu_perf;
+	set_capacity_scale(cpu, capacity);
 
 	pr_info("CPU%d: update cpu_capacity %lu\n",
 		cpu, arch_scale_cpu_capacity(NULL, cpu));