[PATCH v4 3/5] cpufreq: intel_pstate: Tweak the EPP sysfs interface
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STALE2238d
REVIEWED: 1 (1M)
From: Rafael J. Wysocki <hidden>
Date: 2020-09-01 17:40:07
Also in:
lkml
Subsystem:
cpu frequency scaling framework, documentation, intel pstate driver, the rest · Maintainers:
"Rafael J. Wysocki", Viresh Kumar, Jonathan Corbet, Srinivas Pandruvada, Len Brown, Linus Torvalds
Revision v4 of 4 in this series; 1 review trailer.
Revisions (4)
- v1 [diff vs current]
- v2 [diff vs current]
- v3 [diff vs current]
- v4 current
From: "Rafael J. Wysocki" <redacted>
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 <redacted>
Reviewed-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
---
v2 -> v3: New patch
v3 -> v4: Add the R-by from Artem
---
Documentation/admin-guide/pm/intel_pstate.rst | 4 +++-
drivers/cpufreq/intel_pstate.c | 8 ++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/pm/intel_pstate.rst b/Documentation/admin-guide/pm/intel_pstate.rst
index cdd1a9a7f9a2..5072e7064d13 100644
--- a/Documentation/admin-guide/pm/intel_pstate.rst
+++ b/Documentation/admin-guide/pm/intel_pstate.rst@@ -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
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index e540448e0bd0..b308c39b6204 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c@@ -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)
--
2.26.2