linux-kernel - Re: [PATCH V3] cpufreq: Call transition notifier only once for each policy

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Date:   Wed, 24 Apr 2019 09:26:50 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        sparclinux@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH V3] cpufreq: Call transition notifier only once for each policy

On Wed, Apr 24, 2019 at 8:48 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 22-03-19, 11:49, Viresh Kumar wrote:
> > On 21-03-19, 12:45, Peter Zijlstra wrote:
> > > On Wed, Mar 20, 2019 at 10:22:23AM +0530, Viresh Kumar wrote:
>
> > > > 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?
> >
> > My intention was to not add any bug here because of lack of my
> > knowledge of the architecture in question and so I tried to be safe.
> >
> > If you guys think the behavior should be same here as of the tsc, then
> > we can add similar checks here.
>
> I am rebasing this patch over Rafael's patch [1] and wondering if I
> should change anything here.

I guess please repost when my patch makes it into linux-next.

> [1] https://lore.kernel.org/lkml/38900622.ao2n2t5aPS@kreacher/