Messages in this thread | | | Date | Wed, 17 Apr 2024 18:39:00 -0700 | From | Vanshidhar Konda <> | Subject | Re: [PATCH v5 3/5] arm64: Provide an AMU-based version of arch_freq_get_on_cpu |
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On Wed, Apr 17, 2024 at 10:38:46AM +0100, Beata Michalska wrote: >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),
While testing this on AmpereOne system I found that the scaling_cur_freq and cpufreq_cur_freq are inconsistent for nohz_full CPUs that are being throttled (OS requested freq != HW provided freq).
For the test I ran stress-ng workload on 9 cores. All the other cores are idle. I then forced the hardware to throttle the active cores - core won't run at maximum frequency despite a request from the OS. Each core has an independent cpufreq policy.
For the nohz_full CPUs since arch_freq_get_on_cpu bails out. In show_scaling_cur_freq() the next check is to see if cpufreq_driver->set_policy method is implemented. cppc_cpufreq does not implement this method and we just end up returning the policy->cur value. As discussed in other threads, it looks like we want the behavior to be identical to x86 systems. In that case it seems like returning 0 from arch_freq_get_on_cpu is not going to be valid behavior.
Core scaling_cur_freq cpufreq_cur_freq [0]: 2700000 2700000 [1]: 2750000 2750000
nohz_full=2-7 [2]: 3200000 2691000 [3]: 3200000 2645000 [4]: 3200000 2731000 [5]: 3200000 2714000 [6]: 3200000 2466000 [7]: 3200000 2708000
isolcpus=8-11 (no workload applied to core 10-11) [8]: 2700000 2700000 [9]: 2550000 2550000 [10]: 1046875 1046875 [11]: 1096875 1096875
Thanks, Vanshi
>+ * 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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