arm64: Update AMU-based freq scale factor on entering idle

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.
As a consequence, for idle cores, the reported frequency will be the
last one observed before entering the idle state.

Suggested-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
Signed-off-by: Beata Michalska <beata.michalska@arm.com>
Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Reviewed-by: Sumit Gupta <sumitg@nvidia.com>
Link: https://lore.kernel.org/r/20250131162439.3843071-5-beata.michalska@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 28fb004d3103c0326273287233c41e1258b21ad5..a09b0551ec59f67d008a555d6adb3b82a13abbf5 100644 (file)
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -213,6 +213,19 @@ static __always_inline bool amu_fie_cpu_supported(unsigned int cpu)
                cpumask_test_cpu(cpu, amu_fie_cpus);
 }
 
+void arch_cpu_idle_enter(void)
+{
+       unsigned int cpu = smp_processor_id();
+
+       if (!amu_fie_cpu_supported(cpu))
+               return;
+
+       /* Kick in AMU update but only if one has not happened already */
+       if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
+           time_is_before_jiffies(per_cpu(cpu_amu_samples.last_scale_update, cpu)))
+               amu_scale_freq_tick();
+}
+
 #define AMU_SAMPLE_EXP_MS      20
 
 int arch_freq_get_on_cpu(int cpu)