linux-kernel - [PATCH v4 1/4] arch_topology: init capacity_freq

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Date: Fri,  5 Apr 2024 14:33:16 +0100
From: Beata Michalska <beata.michalska@....com>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	ionela.voinescu@....com,
	vanshikonda@...amperecomputing.com
Cc: sudeep.holla@....com,
	will@...nel.org,
	catalin.marinas@....com,
	vincent.guittot@...aro.org,
	sumitg@...dia.com,
	yang@...amperecomputing.com,
	lihuisong@...wei.com
Subject: [PATCH v4 1/4] arch_topology: init capacity_freq_ref to 0

From: Ionela Voinescu <ionela.voinescu@....com>

It's useful to have capacity_freq_ref initialized to 0 for users of
arch_scale_freq_ref() to detect when capacity_freq_ref was not
yet set.

The only scenario affected by this change in the init value is when a
cpufreq driver is never loaded. As a result, the only setter of a
cpu scale factor remains the call of topology_normalize_cpu_scale()
from parse_dt_topology(). There we cannot use the value 0 of
capacity_freq_ref so we have to compensate for its uninitialized state.

Signed-off-by: Ionela Voinescu <ionela.voinescu@....com>
Signed-off-by: Beata Michalska <beata.michalska@....com>
---
 drivers/base/arch_topology.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 024b78a0cfc1..7d4c92cd2bad 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -27,7 +27,7 @@
 static DEFINE_PER_CPU(struct scale_freq_data __rcu *, sft_data);
 static struct cpumask scale_freq_counters_mask;
 static bool scale_freq_invariant;
-DEFINE_PER_CPU(unsigned long, capacity_freq_ref) = 1;
+DEFINE_PER_CPU(unsigned long, capacity_freq_ref) = 0;
 EXPORT_PER_CPU_SYMBOL_GPL(capacity_freq_ref);
 
 static bool supports_scale_freq_counters(const struct cpumask *cpus)
@@ -292,13 +292,15 @@ void topology_normalize_cpu_scale(void)
 
 	capacity_scale = 1;
 	for_each_possible_cpu(cpu) {
-		capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu);
+		capacity = raw_capacity[cpu] *
+			   (per_cpu(capacity_freq_ref, cpu) ?: 1);
 		capacity_scale = max(capacity, capacity_scale);
 	}
 
 	pr_debug("cpu_capacity: capacity_scale=%llu\n", capacity_scale);
 	for_each_possible_cpu(cpu) {
-		capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu);
+		capacity = raw_capacity[cpu] *
+			   (per_cpu(capacity_freq_ref, cpu) ?: 1);
 		capacity = div64_u64(capacity << SCHED_CAPACITY_SHIFT,
 			capacity_scale);
 		topology_set_cpu_scale(cpu, capacity);
-- 
2.25.1