From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Linux PM <linux-pm@vger.kernel.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Doug Smythies <dsmythies@telus.net>,
Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Subject: [PATCH v4 3/5] cpufreq: intel_pstate: Tweak the EPP sysfs interface
Date: Tue, 01 Sep 2020 19:29:55 +0200 [thread overview]
Message-ID: <5280698.oOqPgdve7T@kreacher> (raw)
In-Reply-To: <3748218.V0HrpZKF9g@kreacher>
From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
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>
---
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
next prev parent reply other threads:[~2020-09-01 17:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-01 17:23 [PATCH v4 0/5] cpufreq: intel_pstate: Address some HWP-related oddities Rafael J. Wysocki
2020-09-01 17:25 ` [PATCH v4 1/5] cpufreq: intel_pstate: Refuse to turn off with HWP enabled Rafael J. Wysocki
2020-09-01 17:27 ` [PATCH v4 2/5] cpufreq: intel_pstate: Update cached EPP in the active mode Rafael J. Wysocki
2020-09-01 17:29 ` Rafael J. Wysocki [this message]
2020-09-01 17:37 ` [PATCH v4 4/5] cpufreq: intel_pstate: Add ->offline and ->online callbacks Rafael J. Wysocki
2020-09-01 17:39 ` [PATCH v4 5/5] cpufreq: intel_pstate: Free memory only when turning off Rafael J. Wysocki
2020-09-01 19:07 ` [PATCH v4 0/5] cpufreq: intel_pstate: Address some HWP-related oddities Srinivas Pandruvada
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