@@ -16,6 +16,21 @@ int pcibus_to_node(struct pci_bus *bus);
#include <linux/arch_topology.h>
+#ifdef CONFIG_ARM64_AMU_EXTN
+/*
+ * Replace default function that signals use of counters
+ * for frequency invariance for given CPUs.
+ */
+bool topology_cpu_freq_counters(struct cpumask *cpus);
+#define arch_cpu_freq_counters topology_cpu_freq_counters
+/*
+ * Replace task scheduler's default counter-based
+ * frequency-invariance scale factor setting.
+ */
+void topology_scale_freq_tick(void);
+#define arch_scale_freq_tick topology_scale_freq_tick
+#endif /* CONFIG_ARM64_AMU_EXTN */
+
/* Replace task scheduler's default frequency-invariant accounting */
#define arch_scale_freq_capacity topology_get_freq_scale
@@ -1169,12 +1169,16 @@ bool cpu_has_amu_feat(int cpu)
return cpumask_test_cpu(cpu, &amu_cpus);
}
+/* Initialize the use of AMU counters for frequency invariance */
+extern void init_cpu_freq_invariance_counters(void);
+
static void cpu_amu_enable(struct arm64_cpu_capabilities const *cap)
{
if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) {
pr_info("detected CPU%d: Activity Monitors Unit (AMU)\n",
smp_processor_id());
cpumask_set_cpu(smp_processor_id(), &amu_cpus);
+ init_cpu_freq_invariance_counters();
}
}
@@ -14,6 +14,7 @@
#include <linux/acpi.h>
#include <linux/arch_topology.h>
#include <linux/cacheinfo.h>
+#include <linux/cpufreq.h>
#include <linux/init.h>
#include <linux/percpu.h>
@@ -120,4 +121,177 @@ int __init parse_acpi_topology(void)
}
#endif
+#ifdef CONFIG_ARM64_AMU_EXTN
+#undef pr_fmt
+#define pr_fmt(fmt) "AMU: " fmt
+
+static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale);
+static DEFINE_PER_CPU(u64, arch_const_cycles_prev);
+static DEFINE_PER_CPU(u64, arch_core_cycles_prev);
+static cpumask_var_t amu_fie_cpus;
+
+/* Initialize counter reference per-cpu variables for the current CPU */
+void init_cpu_freq_invariance_counters(void)
+{
+ this_cpu_write(arch_core_cycles_prev,
+ read_sysreg_s(SYS_AMEVCNTR0_CORE_EL0));
+ this_cpu_write(arch_const_cycles_prev,
+ read_sysreg_s(SYS_AMEVCNTR0_CONST_EL0));
+}
+
+static int validate_cpu_freq_invariance_counters(int cpu)
+{
+ u64 max_freq_hz, ratio;
+
+ if (!cpu_has_amu_feat(cpu)) {
+ pr_debug("CPU%d: counters are not supported.\n", cpu);
+ return -EINVAL;
+ }
+
+ if (unlikely(!per_cpu(arch_const_cycles_prev, cpu) ||
+ !per_cpu(arch_core_cycles_prev, cpu))) {
+ pr_debug("CPU%d: cycle counters are not enabled.\n", cpu);
+ return -EINVAL;
+ }
+
+ /* Convert maximum frequency from KHz to Hz and validate */
+ max_freq_hz = cpufreq_get_hw_max_freq(cpu) * 1000;
+ if (unlikely(!max_freq_hz)) {
+ pr_debug("CPU%d: invalid maximum frequency.\n", cpu);
+ return -EINVAL;
+ }
+
+ /*
+ * Pre-compute the fixed ratio between the frequency of the constant
+ * counter and the maximum frequency of the CPU.
+ *
+ * const_freq
+ * arch_max_freq_scale = ---------------- * SCHED_CAPACITY_SCALE²
+ * cpuinfo_max_freq
+ *
+ * We use a factor of 2 * SCHED_CAPACITY_SHIFT -> SCHED_CAPACITY_SCALE²
+ * in order to ensure a good resolution for arch_max_freq_scale for
+ * very low arch timer frequencies (down to the KHz range which should
+ * be unlikely).
+ */
+ ratio = (u64)arch_timer_get_rate() << (2 * SCHED_CAPACITY_SHIFT);
+ ratio = div64_u64(ratio, max_freq_hz);
+ if (!ratio) {
+ WARN_ONCE(1, "System timer frequency too low.\n");
+ return -EINVAL;
+ }
+
+ per_cpu(arch_max_freq_scale, cpu) = (unsigned long)ratio;
+
+ return 0;
+}
+
+static inline int
+enable_policy_freq_counters(int cpu, cpumask_var_t valid_cpus)
+{
+ struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
+
+ if (!policy) {
+ pr_debug("CPU%d: No cpufreq policy found.\n", cpu);
+ return false;
+ }
+
+ if (cpumask_subset(policy->related_cpus, valid_cpus))
+ cpumask_or(amu_fie_cpus, policy->related_cpus,
+ amu_fie_cpus);
+
+ cpufreq_cpu_put(policy);
+
+ return true;
+}
+
+static DEFINE_STATIC_KEY_FALSE(amu_fie_key);
+#define amu_freq_invariant() static_branch_unlikely(&amu_fie_key)
+
+static int __init init_amu_fie(void)
+{
+ cpumask_var_t valid_cpus;
+ bool have_policy = false;
+ int cpu;
+
+ if (!zalloc_cpumask_var(&valid_cpus, GFP_KERNEL) ||
+ !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL))
+ return -ENOMEM;
+
+ for_each_present_cpu(cpu) {
+ if (validate_cpu_freq_invariance_counters(cpu))
+ continue;
+ cpumask_set_cpu(cpu, valid_cpus);
+ have_policy |= enable_policy_freq_counters(cpu, valid_cpus);
+ }
+
+ /*
+ * If we are not restricted by cpufreq policies, we only enable
+ * the use of the AMU feature for FIE if all CPUs support AMU.
+ * Otherwise, enable_policy_freq_counters has already enabled
+ * policy cpus.
+ */
+ if (!have_policy && cpumask_equal(valid_cpus, cpu_present_mask))
+ cpumask_or(amu_fie_cpus, amu_fie_cpus, valid_cpus);
+
+ if (!cpumask_empty(amu_fie_cpus)) {
+ pr_info("CPUs[%*pbl]: counters will be used for FIE.",
+ cpumask_pr_args(amu_fie_cpus));
+ static_branch_enable(&amu_fie_key);
+ }
+
+ free_cpumask_var(valid_cpus);
+
+ return 0;
+}
+late_initcall_sync(init_amu_fie);
+
+bool topology_cpu_freq_counters(struct cpumask *cpus)
+{
+ return amu_freq_invariant() &&
+ cpumask_subset(cpus, amu_fie_cpus);
+}
+
+void topology_scale_freq_tick(void)
+{
+ u64 prev_core_cnt, prev_const_cnt;
+ u64 core_cnt, const_cnt, scale;
+ int cpu = smp_processor_id();
+
+ if (!amu_freq_invariant())
+ return;
+
+ if (!cpumask_test_cpu(cpu, amu_fie_cpus))
+ return;
+
+ const_cnt = read_sysreg_s(SYS_AMEVCNTR0_CONST_EL0);
+ core_cnt = read_sysreg_s(SYS_AMEVCNTR0_CORE_EL0);
+ prev_const_cnt = this_cpu_read(arch_const_cycles_prev);
+ prev_core_cnt = this_cpu_read(arch_core_cycles_prev);
+
+ if (unlikely(core_cnt <= prev_core_cnt ||
+ const_cnt <= prev_const_cnt))
+ goto store_and_exit;
+
+ /*
+ * /\core arch_max_freq_scale
+ * scale = ------- * --------------------
+ * /\const SCHED_CAPACITY_SCALE
+ *
+ * See validate_cpu_freq_invariance_counters() for details on
+ * arch_max_freq_scale and the use of SCHED_CAPACITY_SHIFT.
+ */
+ scale = core_cnt - prev_core_cnt;
+ scale *= this_cpu_read(arch_max_freq_scale);
+ scale = div64_u64(scale >> SCHED_CAPACITY_SHIFT,
+ const_cnt - prev_const_cnt);
+
+ scale = min_t(unsigned long, scale, SCHED_CAPACITY_SCALE);
+ this_cpu_write(freq_scale, (unsigned long)scale);
+
+store_and_exit:
+ this_cpu_write(arch_core_cycles_prev, core_cnt);
+ this_cpu_write(arch_const_cycles_prev, const_cnt);
+}
+#endif /* CONFIG_ARM64_AMU_EXTN */
@@ -29,6 +29,14 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
unsigned long scale;
int i;
+ /*
+ * If the use of counters for FIE is enabled, just return as we don't
+ * want to update the scale factor with information from CPUFREQ.
+ * Instead the scale factor will be updated from arch_scale_freq_tick.
+ */
+ if (arch_cpu_freq_counters(cpus))
+ return;
+
scale = (cur_freq << SCHED_CAPACITY_SHIFT) / max_freq;
for_each_cpu(i, cpus)
@@ -227,5 +227,12 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)
return cpumask_of_node(cpu_to_node(cpu));
}
+#ifndef arch_cpu_freq_counters
+static __always_inline
+bool arch_cpu_freq_counters(struct cpumask *cpus)
+{
+ return false;
+}
+#endif
#endif /* _LINUX_TOPOLOGY_H */
The Frequency Invariance Engine (FIE) is providing a frequency scaling correction factor that helps achieve more accurate load-tracking. So far, for arm and arm64 platforms, this scale factor has been obtained based on the ratio between the current frequency and the maximum supported frequency recorded by the cpufreq policy. The setting of this scale factor is triggered from cpufreq drivers by calling arch_set_freq_scale. The current frequency used in computation is the frequency requested by a governor, but it may not be the frequency that was implemented by the platform. This correction factor can also be obtained using a core counter and a constant counter to get information on the performance (frequency based only) obtained in a period of time. This will more accurately reflect the actual current frequency of the CPU, compared with the alternative implementation that reflects the request of a performance level from the OS. Therefore, implement arch_scale_freq_tick to use activity monitors, if present, for the computation of the frequency scale factor. The use of AMU counters depends on: - CONFIG_ARM64_AMU_EXTN - depents on the AMU extension being present - CONFIG_CPU_FREQ - the current frequency obtained using counter information is divided by the maximum frequency obtained from the cpufreq policy. While it is possible to have a combination of CPUs in the system with and without support for activity monitors, the use of counters for frequency invariance is only enabled for a CPU if all related CPUs (CPUs in the same frequency domain) support and have enabled the core and constant activity monitor counters. In this way, there is a clear separation between the policies for which arch_set_freq_scale (cpufreq based FIE) is used, and the policies for which arch_scale_freq_tick (counter based FIE) is used to set the frequency scale factor. For this purpose, a late_initcall_sync is registered to trigger validation work for policies that will enable or disable the use of AMU counters for frequency invariance. If CONFIG_CPU_FREQ is not defined, the use of counters is enabled on all CPUs only if all possible CPUs correctly support the necessary counters. Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Sudeep Holla <sudeep.holla@arm.com> --- arch/arm64/include/asm/topology.h | 15 +++ arch/arm64/kernel/cpufeature.c | 4 + arch/arm64/kernel/topology.c | 174 ++++++++++++++++++++++++++++++ drivers/base/arch_topology.c | 8 ++ include/linux/topology.h | 7 ++ 5 files changed, 208 insertions(+)