[PATCH] x86/aperfmperf: Make stale CPU frequency response within limits.

[Doug Smythies]

Currently, when the CPU frequency is stale the nominal clock frequency
is returned by calls to arch_freq_get_on_cpu(). Some users are
confused by the high reported frequency when their system is idle
and/or it is above a reduced maximum they set.

This patch will return the policy minimum as the stale frequency reply
from arch_freq_get_on_cpu().

Reported-by: Yang Jie <yang.jie@xxxxxxxxxxxxxxx>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=217597
Signed-off-by: Doug Smythies <dsmythies@xxxxxxxxx>
---
 arch/x86/kernel/cpu/aperfmperf.c | 13 +++++--------
 drivers/cpufreq/cpufreq.c        | 18 ++++++++++++++++++
 include/linux/cpufreq.h          |  5 +++++
 3 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index fdbb5f07448f..44cc96864d94 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -418,9 +418,10 @@ unsigned int arch_freq_get_on_cpu(int cpu)
 	unsigned long last;
 	u64 acnt, mcnt;
 
-	if (!cpu_feature_enabled(X86_FEATURE_APERFMPERF))
-		goto fallback;
-
+	if (!cpu_feature_enabled(X86_FEATURE_APERFMPERF)){
+		freq = cpufreq_quick_get(cpu);
+		return freq ? freq : cpufreq_quick_get_min(cpu);
+	}
 	do {
 		seq = raw_read_seqcount_begin(&s->seq);
 		last = s->last_update;
@@ -433,13 +434,9 @@ unsigned int arch_freq_get_on_cpu(int cpu)
 	 * which covers idle and NOHZ full CPUs.
 	 */
 	if (!mcnt || (jiffies - last) > MAX_SAMPLE_AGE)
-		goto fallback;
+		return cpufreq_quick_get_min(cpu);
 
 	return div64_u64((cpu_khz * acnt), mcnt);
-
-fallback:
-	freq = cpufreq_quick_get(cpu);
-	return freq ? freq : cpu_khz;
 }
 
 static int __init bp_init_aperfmperf(void)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 50bbc969ffe5..a0b24f61a5b0 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1796,6 +1796,24 @@ unsigned int cpufreq_quick_get_max(unsigned int cpu)
 }
 EXPORT_SYMBOL(cpufreq_quick_get_max);
 
+/**
+ * cpufreq_quick_get_min - return the min frequency for a given CPU
+ * @cpu: CPU number
+ */
+unsigned int cpufreq_quick_get_min(unsigned int cpu)
+{
+	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
+	unsigned int ret_freq = 0;
+
+	if (policy) {
+		ret_freq = policy->min;
+		cpufreq_cpu_put(policy);
+	}
+
+	return ret_freq;
+}
+EXPORT_SYMBOL(cpufreq_quick_get_min);
+
 /**
  * cpufreq_get_hw_max_freq - get the max hardware frequency of the CPU
  * @cpu: CPU number
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 172ff51c1b2a..c74dcb5f9263 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -220,6 +220,7 @@ static inline bool policy_is_shared(struct cpufreq_policy *policy)
 unsigned int cpufreq_get(unsigned int cpu);
 unsigned int cpufreq_quick_get(unsigned int cpu);
 unsigned int cpufreq_quick_get_max(unsigned int cpu);
+unsigned int cpufreq_quick_get_min(unsigned int cpu);
 unsigned int cpufreq_get_hw_max_freq(unsigned int cpu);
 void disable_cpufreq(void);
 
@@ -250,6 +251,10 @@ static inline unsigned int cpufreq_quick_get_max(unsigned int cpu)
 {
 	return 0;
 }
+static inline unsigned int cpufreq_quick_get_min(unsigned int cpu)
+{
+	return 0;
+}
 static inline unsigned int cpufreq_get_hw_max_freq(unsigned int cpu)
 {
 	return 0;
-- 
2.25.1