[PATCH v3 3/3] arm64: Update AMU-based frequency scale factor on entering idle

[Beata Michalska <beata.michalska@arm.com>]

Now that the frequency scale factor has been activated for retrieving
current frequency on a given CPU, trigger its update upon entering
idle. This will, to an extent, allow querying last known frequency
in a non-invasive way. It will also improve the frequency scale factor
accuracy when a CPU entering idle did not receive a tick for a while.

Suggested-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
Signed-off-by: Beata Michalska <beata.michalska@arm.com>
---
 arch/arm64/kernel/topology.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 42cb19c31719..77c6ac577cef 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -215,6 +215,18 @@ static struct scale_freq_data amu_sfd = {
 	.set_freq_scale = amu_scale_freq_tick,
 };
 
+void arch_cpu_idle_enter(void)
+{
+	unsigned int cpu = smp_processor_id();
+
+	if (!cpumask_test_cpu(cpu, amu_fie_cpus))
+		return;
+
+	/* Kick in AMU update but only if one has not happned already */
+	if (time_is_before_jiffies(per_cpu(cpu_amu_samples.last_update, cpu)))
+		amu_scale_freq_tick();
+}
+
 #define AMU_SAMPLE_EXP_MS	20
 
 unsigned int arch_freq_get_on_cpu(int cpu)
@@ -242,7 +254,8 @@ unsigned int arch_freq_get_on_cpu(int cpu)
 	 * try an alternative source for the counters (and thus freq scale),
 	 * if available for given policy
 	 */
-	if (time_is_before_jiffies(last_update + msecs_to_jiffies(AMU_SAMPLE_EXP_MS))) {
+	if (!idle_cpu(cpu) &&
+	    time_is_before_jiffies(last_update + msecs_to_jiffies(AMU_SAMPLE_EXP_MS))) {
 		struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
 		int ref_cpu = nr_cpu_ids;
 
-- 
2.25.1