Commit b388eb58 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

cpufreq: intel_pstate: Tweak the EPP sysfs interface 



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: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Acked-by: default avatarSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
parent c27a0ccc

Documentation/admin-guide/pm/intel_pstate.rst

+3 −1
Original line number Diff line number Diff line
@@ -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

drivers/cpufreq/intel_pstate.c

+8 −0
Original line number Diff line number Diff line
@@ -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)

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