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

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Peter Zijlstra" <peterz@infradead.org>,
	"Rafael Wysocki" <rjw@rjwysocki.net>,
	"Russell King" <linux@armlinux.org.uk>,
	"David S. Miller" <davem@davemloft.net>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Linux PM" <linux-pm@vger.kernel.org>,
	"Vincent Guittot" <vincent.guittot@linaro.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	sparclinux@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH V3] cpufreq: Call transition notifier only once for each policy
Date: Wed, 24 Apr 2019 09:26:50 +0200	[thread overview]
Message-ID: <CAJZ5v0jGofnUFKaM5-pRsZAiiQFumGGij8TE=SyX8DT8CUatQg@mail.gmail.com> (raw)
In-Reply-To: <20190424064753.lwfsdeodncaai5oz@vireshk-i7>

On Wed, Apr 24, 2019 at 8:48 AM Viresh Kumar <viresh.kumar@linaro.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/