Messages in this thread | | | Subject | Re: [PATCH v3 6/7] arm64: use activity monitors for frequency invariance | From | Lukasz Luba <> | Date | Wed, 12 Feb 2020 18:59:30 +0000 |
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Hi Ionela,
On 2/11/20 6:45 PM, Ionela Voinescu wrote: > 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 > - (optional) CONFIG_CPU_FREQ - the current frequency obtained using > counter information is divided by the maximum frequency obtained from > the cpufreq policy. But the use of cpufreq policy maximum frequency > is weak and cpu_get_max_freq can be redefined to provide the data > some other way. > > 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 | 16 +++ > arch/arm64/kernel/cpufeature.c | 4 + > arch/arm64/kernel/topology.c | 185 ++++++++++++++++++++++++++++++ > drivers/base/arch_topology.c | 8 ++ > include/linux/topology.h | 7 ++ > 5 files changed, 220 insertions(+) > > diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h > index a4d945db95a2..d910d463cf76 100644 > --- a/arch/arm64/include/asm/topology.h > +++ b/arch/arm64/include/asm/topology.h > @@ -16,6 +16,22 @@ int pcibus_to_node(struct pci_bus *bus); > > #include <linux/arch_topology.h> > > +#ifdef CONFIG_ARM64_AMU_EXTN > +extern unsigned int cpu_get_max_freq(unsigned int cpu); > +/* > + * 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 > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 029a473ad273..a4620b269b56 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1172,12 +1172,16 @@ bool cpu_has_amu_feat(int cpu) > return false; > } > > +/* 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(); > } > } > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index fa9528dfd0ce..3f6e379f07b3 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -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 +121,188 @@ 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; > + > +/* Obtain max frequency (in KHz) as reported by hardware */ > +__weak unsigned int cpu_get_max_freq(unsigned int cpu) > +{ > + return 0; > +} > + > +#ifdef CONFIG_CPU_FREQ > +/* Replace max frequency getter with cpufreq based function */ > +#define cpu_get_max_freq cpufreq_get_hw_max_freq > +#endif
Can we just use cpufreq_get_hw_max_freq()? We have cpufreq_get_hw_max_freq returning 0 in such case, so it should be OK.
Is there a possibility that some platform which has !CONFIG_CPU_FREQ would define its own cpu_get_max_freq() overwriting the weak function above? Based on the code which checks 'if (unlikely(!max_freq_hz))' it should, otherwise 'valid_cpus' is not set.
I would assume that we won't see such platform, interested in AMU freq invariance without CONFIG_CPU_FREQ.
We already have a lot of these defines or __weak functions, which is hard to follow.
Apart from that and the issue with cpu_has_amu_feat() it looks good.
> + > +/* 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)) {
As Suzuki pointed out with 'amu_cpus', make sure we read a one instance of mask here.
Regards, Lukasz
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