Messages in this thread Patch in this message | | | From | Beata Michalska <> | Subject | [PATCH v5 3/5] arm64: Provide an AMU-based version of arch_freq_get_on_cpu | Date | Wed, 17 Apr 2024 10:38:46 +0100 |
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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@arm.com> Signed-off-by: Beata Michalska <beata.michalska@arm.com> --- arch/arm64/kernel/topology.c | 110 +++++++++++++++++++++++++++++++---- 1 file changed, 100 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index 3c814a278534..475fdbf3032a 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -17,6 +17,7 @@ #include <linux/cpufreq.h> #include <linux/init.h> #include <linux/percpu.h> +#include <linux/sched/isolation.h> #include <asm/cpu.h> #include <asm/cputype.h> @@ -88,18 +89,28 @@ int __init parse_acpi_topology(void) * initialized. */ static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale) = 1UL << (2 * SCHED_CAPACITY_SHIFT); -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; +struct amu_cntr_sample { + u64 arch_const_cycles_prev; + u64 arch_core_cycles_prev; + unsigned long last_update; +}; + +static DEFINE_PER_CPU_SHARED_ALIGNED(struct amu_cntr_sample, cpu_amu_samples); + void update_freq_counters_refs(void) { - this_cpu_write(arch_core_cycles_prev, read_corecnt()); - this_cpu_write(arch_const_cycles_prev, read_constcnt()); + struct amu_cntr_sample *amu_sample = this_cpu_ptr(&cpu_amu_samples); + + amu_sample->arch_core_cycles_prev = read_corecnt(); + amu_sample->arch_const_cycles_prev = read_constcnt(); } static inline bool freq_counters_valid(int cpu) { + struct amu_cntr_sample *amu_sample = per_cpu_ptr(&cpu_amu_samples, cpu); + if ((cpu >= nr_cpu_ids) || !cpumask_test_cpu(cpu, cpu_present_mask)) return false; @@ -108,8 +119,8 @@ static inline bool freq_counters_valid(int cpu) return false; } - if (unlikely(!per_cpu(arch_const_cycles_prev, cpu) || - !per_cpu(arch_core_cycles_prev, cpu))) { + if (unlikely(!amu_sample->arch_const_cycles_prev || + !amu_sample->arch_core_cycles_prev)) { pr_debug("CPU%d: cycle counters are not enabled.\n", cpu); return false; } @@ -152,17 +163,22 @@ void freq_inv_set_max_ratio(int cpu, u64 max_rate) static void amu_scale_freq_tick(void) { + struct amu_cntr_sample *amu_sample = this_cpu_ptr(&cpu_amu_samples); u64 prev_core_cnt, prev_const_cnt; u64 core_cnt, const_cnt, scale; - prev_const_cnt = this_cpu_read(arch_const_cycles_prev); - prev_core_cnt = this_cpu_read(arch_core_cycles_prev); + prev_const_cnt = amu_sample->arch_const_cycles_prev; + prev_core_cnt = amu_sample->arch_core_cycles_prev; update_freq_counters_refs(); - const_cnt = this_cpu_read(arch_const_cycles_prev); - core_cnt = this_cpu_read(arch_core_cycles_prev); + const_cnt = amu_sample->arch_const_cycles_prev; + core_cnt = amu_sample->arch_core_cycles_prev; + /* + * This should not happen unless the AMUs have been reset and the + * counter values have not been restored - unlikely + */ if (unlikely(core_cnt <= prev_core_cnt || const_cnt <= prev_const_cnt)) return; @@ -182,6 +198,8 @@ static void amu_scale_freq_tick(void) scale = min_t(unsigned long, scale, SCHED_CAPACITY_SCALE); this_cpu_write(arch_freq_scale, (unsigned long)scale); + + amu_sample->last_update = jiffies; } static struct scale_freq_data amu_sfd = { @@ -189,6 +207,78 @@ static struct scale_freq_data amu_sfd = { .set_freq_scale = amu_scale_freq_tick, }; +static __always_inline bool amu_fie_cpu_supported(unsigned int cpu) +{ + return cpumask_available(amu_fie_cpus) && + cpumask_test_cpu(cpu, amu_fie_cpus); +} + +#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); + 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; -- 2.25.1
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