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

On Wed, 2016-06-08 at 02:42 +0200, Rafael J. Wysocki wrote:

On Wed, Jun 8, 2016 at 2:38 AM, Srinivas Pandruvada
[off-list ref] wrote:

quoted

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

quoted

---
 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-

quoted

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-

quoted

pstate.scaling;

+       else
+               policy->cpuinfo.max_freq =
+                       cpu->pstate.turbo_pstate * cpu-

quoted

pstate.scaling;

+
        intel_pstate_init_acpi_perf_limits(policy);
        policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
        cpumask_set_cpu(policy->cpu, policy->cpus);
--