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SubjectRe: [PATCH V3] cpufreq: Call transition notifier only once for each policy
On Wed, Mar 20, 2019 at 10:22:23AM +0530, Viresh Kumar wrote:
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 3fae23834069..b2fe665878f7 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -958,10 +958,15 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> struct cpufreq_freqs *freq = data;
> unsigned long *lpj;
>
> + if (WARN_ON_ONCE(cpumask_weight(freq->policy->related_cpus) != 1)) {
> + mark_tsc_unstable("cpufreq changes: related CPUs affected");

I suspect this is a big fat nop, but it won't hurt.

> + return 0;
> + }
> +
> lpj = &boot_cpu_data.loops_per_jiffy;
> #ifdef CONFIG_SMP
> if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> - lpj = &cpu_data(freq->cpu).loops_per_jiffy;
> + lpj = &cpu_data(freq->policy->cpu).loops_per_jiffy;
> #endif
>
> if (!ref_freq) {
> @@ -977,7 +982,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> if (!(freq->flags & CPUFREQ_CONST_LOOPS))
> mark_tsc_unstable("cpufreq changes");
>
> - set_cyc2ns_scale(tsc_khz, freq->cpu, rdtsc());
> + set_cyc2ns_scale(tsc_khz, freq->policy->cpu, rdtsc());
> }
>
> return 0;

Just wondering, since we say x86 cpufreq handlers will only have a
single CPU here,

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 65e4559eef2f..1ac8c710cccc 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6649,10 +6649,8 @@ static void kvm_hyperv_tsc_notifier(void)
> }
> #endif
>
> -static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> - void *data)
> +static void __kvmclock_cpufreq_notifier(struct cpufreq_freqs *freq, int cpu)
> {
> - struct cpufreq_freqs *freq = data;
> struct kvm *kvm;
> struct kvm_vcpu *vcpu;
> int i, send_ipi = 0;
> @@ -6696,17 +6694,12 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va
> *
> */
>
> - if (val == CPUFREQ_PRECHANGE && freq->old > freq->new)
> - return 0;
> - if (val == CPUFREQ_POSTCHANGE && freq->old < freq->new)
> - return 0;
> -
> - smp_call_function_single(freq->cpu, tsc_khz_changed, freq, 1);
> + smp_call_function_single(cpu, tsc_khz_changed, freq, 1);
>
> spin_lock(&kvm_lock);
> list_for_each_entry(kvm, &vm_list, vm_list) {
> kvm_for_each_vcpu(i, vcpu, kvm) {
> - if (vcpu->cpu != freq->cpu)
> + if (vcpu->cpu != cpu)
> continue;
> kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
> if (vcpu->cpu != smp_processor_id())
> @@ -6728,8 +6721,24 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va
> * guest context is entered kvmclock will be updated,
> * so the guest will not see stale values.
> */
> - smp_call_function_single(freq->cpu, tsc_khz_changed, freq, 1);
> + smp_call_function_single(cpu, tsc_khz_changed, freq, 1);
> }
> +}
> +
> +static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> + void *data)
> +{
> + struct cpufreq_freqs *freq = data;
> + int cpu;
> +
> + if (val == CPUFREQ_PRECHANGE && freq->old > freq->new)
> + return 0;
> + if (val == CPUFREQ_POSTCHANGE && freq->old < freq->new)
> + return 0;
> +
> + for_each_cpu(cpu, freq->policy->cpus)
> + __kvmclock_cpufreq_notifier(freq, cpu);
> +
> return 0;
> }
>

Then why to we pretend otherwise here?

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