Re: [PATCH 2/2] cpufreq: intel_pstate: Fix set_policy interface for no_turbo

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

On Wed, 2016-06-08 at 02:42 +0200, Rafael J. Wysocki wrote:
> On Wed, Jun 8, 2016 at 2:38 AM, Srinivas Pandruvada
> <srinivas.pandruvada@linux.intel.com> wrote:
> > 
> > When turbo is disabled, the set_policy interface is broken.
> > For example, when turbo is disabled and
> > cpuinfo.max = 2900000 (full max turbo frequency)
> > Setting the limits results in frequency less than settings:
> > Set 1000000 KHz results in 0700000 KHz
> > Set 1500000 KHz results in 1100000 KHz
> > Set 2000000 KHz results in  1500000 KHz
> > 
> > This is because limits->max_perf fraction is calculated using max
> > turbo frequency as the reference, but when the max P-State is
> > capped in the function intel_pstate_get_min_max, the reference
> > is not the max turbo P-State. This results in reducing max
> > P-State.
> > 
> > One option is to always use max turbo as reference for calculating
> > limits. But this will not be correct. By definition the
> > intel_pstate
> > sysfs limits, shows percentage of available performance. So when
> > BIOS has disabled turbo, the available performance is max non
> > turbo.
> > So the max_perf_pct should still show 100%.
> > 
> > Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel
> > .com>
> I guess we need this in -stable?
Yes.
> 
> If so, all of them, or is there a specific starting point?
I think this is from (even in 3.10, it should have the same behavior
looking at the code).

Thanks,
Srinivas

> 
> > 
> > ---
> >  drivers/cpufreq/intel_pstate.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/cpufreq/intel_pstate.c
> > b/drivers/cpufreq/intel_pstate.c
> > index 724b905..2116666 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -1561,8 +1561,14 @@ static int intel_pstate_cpu_init(struct
> > cpufreq_policy *policy)
> > 
> >         /* cpuinfo and default policy values */
> >         policy->cpuinfo.min_freq = cpu->pstate.min_pstate * cpu-
> > >pstate.scaling;
> > -       policy->cpuinfo.max_freq =
> > -               cpu->pstate.turbo_pstate * cpu->pstate.scaling;
> > +       update_turbo_state();
> > +       if (limits->turbo_disabled)
> > +               policy->cpuinfo.max_freq =
> > +                       cpu->pstate.max_pstate * cpu-
> > >pstate.scaling;
> > +       else
> > +               policy->cpuinfo.max_freq =
> > +                       cpu->pstate.turbo_pstate * cpu-
> > >pstate.scaling;
> > +
> >         intel_pstate_init_acpi_perf_limits(policy);
> >         policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
> >         cpumask_set_cpu(policy->cpu, policy->cpus);
> > --