linux-kernel - [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support

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Date:   Thu,  6 Jul 2017 10:49:40 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-pm@...r.kernel.org, linux@....linux.org.uk,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Juri Lelli <juri.lelli@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>
Subject: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support

A frequency-invariant load-tracking solution based on cpufreq transition
notifier will not work for future fast frequency switching policies.
That is why a different solution is presented with this patch.

Let cpufreq call the function arch_set_freq_scale() to pass the current
frequency, the max supported frequency and the cpumask of the related
cpus to a consumer (an arch) which defines arch_set_freq_scale().

The consumer has to associate arch_set_freq_scale with the name of its
own implementation foo_set_freq_scale() to overwrite the empty standard
definition in drivers/cpufreq/cpufreq.c.
An arch could do this in one of its arch-specific header files
(e.g. arch/$ARCH/include/asm/topology.h) which gets included in
drivers/cpufreq/cpufreq.c.

In case arch_set_freq_scale() is not defined (and because of the
pr_debug() drivers/cpufreq/cpufreq.c is not compiled with -DDEBUG) the
function cpufreq_set_freq_scale() gets compiled out.

Cc: Rafael J. Wysocki <rjw@...ysocki.net>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
---
 drivers/cpufreq/cpufreq.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 9bf97a366029..a04c5886a5ce 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -347,6 +347,28 @@ static void __cpufreq_notify_transition(struct cpufreq_policy *policy,
 	}
 }
 
+/*********************************************************************
+ *           FREQUENCY INVARIANT CPU CAPACITY SUPPORT                *
+ *********************************************************************/
+
+#ifndef arch_set_freq_scale
+static void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
+				unsigned long max_freq)
+{}
+#endif
+
+static void cpufreq_set_freq_scale(struct cpufreq_policy *policy,
+				   struct cpufreq_freqs *freqs)
+{
+	unsigned long cur_freq = freqs ? freqs->new : policy->cur;
+	unsigned long max_freq = policy->cpuinfo.max_freq;
+
+	pr_debug("cpus %*pbl cur/cur max freq %lu/%lu kHz\n",
+		 cpumask_pr_args(policy->related_cpus), cur_freq, max_freq);
+
+	arch_set_freq_scale(policy->related_cpus, cur_freq, max_freq);
+}
+
 /**
  * cpufreq_notify_transition - call notifier chain and adjust_jiffies
  * on frequency transition.
@@ -405,6 +427,8 @@ void cpufreq_freq_transition_begin(struct cpufreq_policy *policy,
 
 	spin_unlock(&policy->transition_lock);
 
+	cpufreq_set_freq_scale(policy, freqs);
+
 	cpufreq_notify_transition(policy, freqs, CPUFREQ_PRECHANGE);
 }
 EXPORT_SYMBOL_GPL(cpufreq_freq_transition_begin);
@@ -2203,6 +2227,8 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
 	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
 			CPUFREQ_NOTIFY, new_policy);
 
+	cpufreq_set_freq_scale(new_policy, NULL);
+
 	policy->min = new_policy->min;
 	policy->max = new_policy->max;
 
-- 
2.11.0