Re: [PATCH][RFC] ACPI: add "processor.broadcast_ppc" hook to broadcast _PPC to all online CPUs

[Rafael J. Wysocki]

On Sat, Feb 9, 2019 at 12:54 PM Chen Yu <yu.c.chen@xxxxxxxxx> wrote:
>
> On Dell Inc. XPS13 9333, the BIOS changes the value of
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE at runtime (e.g., when
> the power source changes), the maximum frequency of the
> CPU is not updated accordingly. This is due to the policy's
> cpuinfo.max is not updated when _PPC notifier fires.
>
> Fix this problem by updating the policy's cpuinfo.max
> and broadcast the _PPC notifier to all online CPUs.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200759
> Reported-and-tested-by: Gabriele Mazzotta <gabriele.mzt@xxxxxxxxx>
> Originally-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> ---
>  drivers/acpi/processor_perflib.c | 16 ++++++++++++++--
>  drivers/cpufreq/cpufreq.c        |  2 ++
>  drivers/cpufreq/intel_pstate.c   | 15 ++++++++++++++-
>  3 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c
> index a303fd0e108c..737dbf5aa7f7 100644
> --- a/drivers/acpi/processor_perflib.c
> +++ b/drivers/acpi/processor_perflib.c
> @@ -63,6 +63,10 @@ module_param(ignore_ppc, int, 0644);
>  MODULE_PARM_DESC(ignore_ppc, "If the frequency of your machine gets wrongly" \
>                  "limited by BIOS, this should help");
>
> +static int broadcast_ppc;
> +module_param(broadcast_ppc, int, 0644);
> +MODULE_PARM_DESC(broadcast_ppc, "Broadcast the ppc to all online CPUs");
> +
>  #define PPC_REGISTERED   1
>  #define PPC_IN_USE       2
>
> @@ -180,8 +184,16 @@ void acpi_processor_ppc_has_changed(struct acpi_processor *pr, int event_flag)
>                 else
>                         acpi_processor_ppc_ost(pr->handle, 0);
>         }
> -       if (ret >= 0)
> -               cpufreq_update_policy(pr->id);
> +       if (ret >= 0) {
> +               if (broadcast_ppc) {
> +                       int cpu;
> +
> +                       for_each_possible_cpu(cpu)
> +                               cpufreq_update_policy(cpu);
> +               } else {
> +                       cpufreq_update_policy(pr->id);
> +               }
> +       }
>  }
>
>  int acpi_processor_get_bios_limit(int cpu, unsigned int *limit)
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index e35a886e00bc..95e08816b512 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2237,6 +2237,8 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
>
>         policy->min = new_policy->min;
>         policy->max = new_policy->max;
> +       policy->cpuinfo.max_freq = new_policy->cpuinfo.max_freq;
> +       policy->cpuinfo.min_freq = new_policy->cpuinfo.min_freq;
>         trace_cpu_frequency_limits(policy);
>
>         policy->cached_target_freq = UINT_MAX;
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index dd66decf2087..e1881313c396 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -2081,11 +2081,24 @@ static void intel_pstate_adjust_policy_max(struct cpufreq_policy *policy,
>
>  static int intel_pstate_verify_policy(struct cpufreq_policy *policy)
>  {
> +       int max_freq;
>         struct cpudata *cpu = all_cpu_data[policy->cpu];
>
>         update_turbo_state();

Well, update_turbo_state() should handle the case at hand already.

That's what it's for actually: It checks if
MSR_IA32_MISC_ENABLE_TURBO_DISABLE is set and sets
global.turbo_disabled is that's the case.

Why isn't that sufficient?

> +       max_freq = intel_pstate_get_max_freq(cpu);
> +
> +       if (acpi_ppc && policy->max == policy->cpuinfo.max_freq &&
> +           max_freq != policy->cpuinfo.max_freq) {
> +               /*
> +                * System was not running under any constraints, but the
> +                * current max possible frequency is changed. So reset
> +                * policy limits.
> +                */
> +               policy->cpuinfo.max_freq = policy->max = max_freq;
> +       }

Why does policy->cpuinfo.max_freq need to be updated?

> +
>         cpufreq_verify_within_limits(policy, policy->cpuinfo.min_freq,
> -                                    intel_pstate_get_max_freq(cpu));
> +                                    max_freq);
>
>         if (policy->policy != CPUFREQ_POLICY_POWERSAVE &&
>             policy->policy != CPUFREQ_POLICY_PERFORMANCE)
> --