With the Frequency Invariance Engine (FIE) being already wired up with...
sched tick and making use of relevant (core counter and constant
counter) AMU counters, getting the current frequency for a given CPU,
can be achieved by utilizing the frequency scale factor which reflects
an average CPU frequency for the last tick period length.
The solution is partially based on APERF/MPERF implementation of
arch_freq_get_on_cpu.
Suggested-by: Ionela Voinescu <ionela.voinescu@xxxxxxx>
Signed-off-by: Beata Michalska <beata.michalska@xxxxxxx>
---
arch/arm64/kernel/topology.c | 110 +++++++++++++++++++++++++++++++----
1 file changed, 100 insertions(+), 10 deletions(-)
+One question here.
+#define AMU_SAMPLE_EXP_MS 20
+
+unsigned int arch_freq_get_on_cpu(int cpu)
+{
+ struct amu_cntr_sample *amu_sample;
+ unsigned int start_cpu = cpu;
+ unsigned long last_update;
+ unsigned int freq = 0;
+ u64 scale;
+
+ if (!amu_fie_cpu_supported(cpu) || !arch_scale_freq_ref(cpu))
+ return 0;
+
+retry:
+ amu_sample = per_cpu_ptr(&cpu_amu_samples, cpu);
+
+ last_update = amu_sample->last_update;
+
+ /*
+ * For those CPUs that are in full dynticks mode,
+ * and those that have not seen tick for a while
+ * try an alternative source for the counters (and thus freq scale),
+ * if available, for given policy:
+ * 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))) {
+ struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);start_cpu is only used here. looks like we can s/start_cpu/cpu/ and remove its definition above?
+ int ref_cpu = cpu;
+
+ if (!policy)
+ goto leave;
+
+ if (!policy_is_shared(policy)) {
+ cpufreq_cpu_put(policy);
+ goto leave;
+ }
+
+ do {
+ ref_cpu = cpumask_next_wrap(ref_cpu, policy->cpus,
+ start_cpu, false);
+
+ } while (ref_cpu < nr_cpu_ids && idle_cpu(ref_cpu));
+
+ cpufreq_cpu_put(policy);
+
+ if (ref_cpu >= nr_cpu_ids)
+ /* No alternative to pull info from */
+ goto leave;
+
+ cpu = ref_cpu;
+ goto retry;
+ }
+ /*
+ * Reversed computation to the one used to determine
+ * the arch_freq_scale value
+ * (see amu_scale_freq_tick for details)
+ */
+ scale = arch_scale_freq_capacity(cpu);
+ freq = scale * arch_scale_freq_ref(cpu);
+ freq >>= SCHED_CAPACITY_SHIFT;
+leave:
+ return freq;
+}
+
static void amu_fie_setup(const struct cpumask *cpus)
{
int cpu;