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cpufreq: intel_pstate: Tweak the EPP sysfs interface

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Modify the EPP sysfs interface to reject attempts to change the EPP
to values different from 0 ("performance") in the active mode with
the "performance" policy (ie. scaling_governor set to "performance"),
to avoid situations in which the kernel appears to discard data
passed to it via the EPP sysfs attribute.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
This commit is contained in:
Rafael J. Wysocki 2020-08-27 14:32:12 +02:00
parent c27a0ccc3c
commit b388eb58ce
2 changed files with 11 additions and 1 deletions
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4
Documentation/admin-guide/pm/intel_pstate.rst
View File

@ -123,7 +123,9 @@ Energy-Performance Bias (EPB) knob (otherwise), which means that the processor's
internal P-state selection logic is expected to focus entirely on performance.
This will override the EPP/EPB setting coming from the ``sysfs`` interface
(see `Energy vs Performance Hints`_ below).
(see `Energy vs Performance Hints`_ below). Moreover, any attempts to change
the EPP/EPB to a value different from 0 ("performance") via ``sysfs`` in this
configuration will be rejected.
Also, in this configuration the range of P-states available to the processor's
internal P-state selection logic is always restricted to the upper boundary

8
drivers/cpufreq/intel_pstate.c
View File

@ -684,6 +684,14 @@ static int intel_pstate_set_energy_pref_index(struct cpudata *cpu_data,
else if (epp == -EINVAL)
epp = epp_values[pref_index - 1];
/*
* To avoid confusion, refuse to set EPP to any values different
* from 0 (performance) if the current policy is "performance",
* because those values would be overridden.
*/
if (epp > 0 && cpu_data->policy == CPUFREQ_POLICY_PERFORMANCE)
return -EBUSY;
ret = intel_pstate_set_epp(cpu_data, epp);
} else {
if (epp == -EINVAL)