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From:   David Dai <davidai@google.com>
Date:   Wed, 5 Apr 2023 15:42:28 -0700
Message-ID: <CABN1KCJ0Tk5ah33zKpksq4Ftqa8Eh+V3bGZRMRAv-XrmakT1Og@mail.gmail.com>
Subject: Re: [RFC PATCH 6/6] cpufreq: add kvm-cpufreq driver
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Saravana Kannan <saravanak@google.com>,
        kernel-team@android.com, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org
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On Wed, Apr 5, 2023 at 1:23=E2=80=AFAM Peter Zijlstra <peterz@infradead.org=
> wrote:
>
> On Thu, Mar 30, 2023 at 03:43:41PM -0700, David Dai wrote:
>
> > +struct remote_data {
> > +     int ret;
> > +     struct cpufreq_frequency_table *table;
> > +};
> > +
> > +static void remote_get_freqtbl_num_entries(void *data)
> > +{
> > +     struct arm_smccc_res hvc_res;
> > +     u32 freq =3D 1UL;
> > +     int *idx =3D data;
> > +
> > +     while (freq !=3D CPUFREQ_TABLE_END) {
> > +             arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_GET_CPUFREQ=
_TBL_FUNC_ID,
> > +                             *idx, &hvc_res);
> > +             if (hvc_res.a0) {
> > +                     *idx =3D -ENODEV;
> > +                     return;
> > +             }
> > +             freq =3D hvc_res.a1;
> > +             (*idx)++;
> > +     }
> > +}
> > +
> > +static int kvm_cpufreq_get_freqtbl_num_entries(int cpu)
> > +{
> > +     int num_entries =3D 0;
> > +
> > +     smp_call_function_single(cpu, remote_get_freqtbl_num_entries, &nu=
m_entries, true);
> > +     return num_entries;
> > +}
> > +
> > +static void remote_populate_freqtbl(void *data)
> > +{
> > +     struct arm_smccc_res hvc_res;
> > +     struct remote_data *freq_data =3D data;
> > +     struct cpufreq_frequency_table *pos;
> > +     struct cpufreq_frequency_table *table =3D freq_data->table;
> > +     int idx;
> > +
> > +     cpufreq_for_each_entry_idx(pos, table, idx) {
> > +             arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_GET_CPUFREQ=
_TBL_FUNC_ID,
> > +                             idx, &hvc_res);
> > +             if (hvc_res.a0) {
> > +                     freq_data->ret =3D -ENODEV;
> > +                     return;
> > +             }
> > +             pos->frequency =3D hvc_res.a1;
> > +     }
> > +     freq_data->ret =3D 0;
> > +}
> > +
> > +static int kvm_cpufreq_populate_freqtbl(struct cpufreq_frequency_table=
       *table, int cpu)
> > +{
> > +     struct remote_data freq_data;
> > +
> > +     freq_data.table =3D table;
> > +     smp_call_function_single(cpu, remote_populate_freqtbl, &freq_data=
, true);
> > +     return freq_data.ret;
> > +}
>

Hi Peter,

Thanks for taking the time to review!

> *WHY* are you sending IPIs to do a hypercall ?!?
>
> You can simply have the hypercall tell what vCPU you're doing this for.
>

We=E2=80=99ll remove all the code that=E2=80=99s making IPI calls and switc=
h over to
populating the frequency tables in the device tree when we move from
RFC to PATCH. It is here for now to make it easier for others to
cherry-pick and test the series without needing more changes to their
VMM.

Thanks,
David