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From: Beata Michalska <beata.michalska@arm.com>
To: linux-kernel@vger.kernel.org,
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Subject: [PATCH v6 4/4] arm64: Update AMU-based freq scale factor on  entering idle
Date: Mon,  3 Jun 2024 09:21:54 +0100
Message-Id: <20240603082154.3830591-5-beata.michalska@arm.com>
In-Reply-To: <20240603082154.3830591-1-beata.michalska@arm.com>
References: <20240603082154.3830591-1-beata.michalska@arm.com>
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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>
---
 arch/arm64/kernel/topology.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 2c002d2c3e0b..56c5b2e632b4 100644
--- 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_update, cpu)))
+		amu_scale_freq_tick();
+}
+
 #define AMU_SAMPLE_EXP_MS	20
 
 unsigned int arch_freq_get_on_cpu(int cpu)
@@ -239,8 +252,8 @@ unsigned int arch_freq_get_on_cpu(int cpu)
 	 * this boils down to identifying an active cpu within the same freq
 	 * domain, if any.
 	 */
-	if (!housekeeping_cpu(cpu, HK_TYPE_TICK) ||
-	    time_is_before_jiffies(last_update + msecs_to_jiffies(AMU_SAMPLE_EXP_MS))) {
+	if (!housekeeping_cpu(cpu, HK_TYPE_TICK) || (!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 = cpu;
 
-- 
2.25.1