Re: [PATCH 2/2][RFC v2] ACPI: Update cpuinfo.max after bootup if necessary

[Yu Chen <yu.c.chen@intel.com>]

On Thu, Feb 28, 2019 at 11:56:48PM +0100, Rafael J. Wysocki wrote:
> On Thu, Feb 28, 2019 at 6:59 PM Chen Yu <yu.c.chen@intel.com> 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 when
> > necessary.
> >
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=200759
> > Reported-and-tested-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
> > Originally-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> > Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> > ---
> >  drivers/cpufreq/cpufreq.c      |  2 ++
> >  drivers/cpufreq/intel_pstate.c | 15 +++++++++++++--
> >  2 files changed, 15 insertions(+), 2 deletions(-)
> >
> > 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..841c74f69f66 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -2081,11 +2081,17 @@ 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();
> > +       max_freq = intel_pstate_get_max_freq(cpu);
> > +
> > +       if (acpi_ppc && max_freq != policy->cpuinfo.max_freq)
> > +               policy->cpuinfo.max_freq = policy->max = max_freq;
> 
> Updating cpuinfo.max_freq here only causes the current limit to be
> reported via sysfs, because intel_pstate doesn't actually use
> cpuinfo.max_freq for anything and the core doesn't enforce it as a
> limit.
> 
> All of the computations in the active mode in the driver actually use
> the current limit anyway AFAICS.
>
Yes, but it looks like we should also take care of the cpuinfo.max
if it changes, I searched the code, it seems that other components
might use the policy's cpuinfo.max for some purpose. They might use
cpufreq_cpu_get() to get the policy, and use the cpuinfo.max_freq
directly, no matter what the mode intel_pstate is in. Such as kvm
might use it as the max tsc khz if the tsc is not constant. And i915
might consider the cpuinfo.max_freq to adjust the IA frequency on
gen6 platforms. So changing cpuinfo.max might also impact not only
cpufreq but also other components too.
> > +
> >         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)
> > @@ -2192,11 +2198,16 @@ static struct cpufreq_driver intel_pstate = {
> >
> >  static int intel_cpufreq_verify_policy(struct cpufreq_policy *policy)
> >  {
> > +       int max_freq;
> >         struct cpudata *cpu = all_cpu_data[policy->cpu];
> >
> >         update_turbo_state();
> > +       max_freq = intel_pstate_get_max_freq(cpu);
> > +
> > +       if (acpi_ppc && max_freq != policy->cpuinfo.max_freq)
> > +               policy->cpuinfo.max_freq = policy->max = max_freq;
> 
> In this case (passive mode) updating cpuinfo.max_freq will actually
> cause governors to use the new value in computations, so the P-state
> selection will work somewhat differently, but that isn't really
> consistent with what acpi-cpufreq does and with setting no_turbo in
> the intel_pstate sysfs to 1 without this patch.
> 
> With acpi-cpufreq cpuinfo.max_freq is always the max frequency in the
> _PSS table regardless of what the _PSS limit is.  Also setting
> no_turbo to 1 in intel_pstate without this patch doesn't cause
> cpuinfo.max_freq to change and I don't really think that it should.
> 
> I would be tempted to always initialize cpuinfo.max_freq to the max
> turbo frequency, but there is a concern about systems in which
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE is never set on the fly (just in
> the BIOS setup as it should be) and where it doesn't make sense to
> consider turbo frequencies at all.
Ok, maybe we can check the bit during boot(consider BIOS's setting)?
> 
> >         cpufreq_verify_within_limits(policy, policy->cpuinfo.min_freq,
> > -                                    intel_pstate_get_max_freq(cpu));
> > +                                    max_freq);
> >
> >         intel_pstate_adjust_policy_max(policy, cpu);
> >
> > --
> 
> It looks like I need to think about this a bit more.
Ok, I'll test the patch you sent out.

Thanks,
Yu