linux-kernel - [PATCH] arch_topology: init capacity_freq

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Message-Id: <20240827154818.1195849-1-ionela.voinescu@arm.com>
Date: Tue, 27 Aug 2024 16:48:18 +0100
From: Ionela Voinescu <ionela.voinescu@....com>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	sudeep.holla@....com,
	catalin.marinas@....com,
	vincent.guittot@...aro.org,
	beata.michalska@....com
Cc: rafael@...nel.org,
	viresh.kumar@...aro.org,
	dietmar.eggemann@....com,
	pierre.gondois@....com
Subject: [PATCH] arch_topology: init capacity_freq_ref to 0

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>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Reviewed-by: Sudeep Holla <sudeep.holla@....com>
---

Hi,

This patch was previously part of the patch-set at [1], but we thought
it's best to separate the standalone patches in that set to make
further review easier on the remaining topics.

Based on v6.11-rc5 and tested on Juno with and without a cpufreq driver.

[1] https://lore.kernel.org/lkml/20240603082154.3830591-2-beata.michalska@arm.com/

Thanks,
Ionela.

 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 75fcb75d5515..c49ef1a712f4 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -28,7 +28,7 @@
 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)
@@ -293,13 +293,15 @@ 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