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cpufreq: cppc: drop invariance when FIE is disabled

PATCH In review Penghe Geng 2 participants 2 messages Feb 20 – Feb 25

Subsystems (3)
Stable branch CPU frequency scaling framework CPU frequency drivers - CPPC cpufreq
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Penghe Geng

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#0 lore raw

PATCH 1/1 cpufreq: cppc: drop invariance when FIE is disabled

CONFIG_ACPI_CPPC_CPUFREQ_FIE gates CPPC counter-based frequency invariance support. When FIE is disabled, the CPPC driver does not register a frequency scale source, but cpufreq_register_driver() still enables cpufreq_freq_invariance for target/fast-switch drivers.

Disable cpufreq frequency invariance after CPPC driver registration when FIE is disabled. This avoids scheduler behavior mismatch when no invariance updates are provided, which can cause major performance regressions on sensitive platforms.

Export cpufreq_disable_freq_invariance() so modular cppc_cpufreq can call it.

Fixes 1eb5dde674f5 ("cpufreq: CPPC: Add support for frequency invariance")
Cc [email protected]
Signed-off-by Penghe Geng <[email protected]>
---
 drivers/cpufreq/cppc_cpufreq.c | 4 ++++
 drivers/cpufreq/cpufreq.c      | 8 ++++++++
 include/linux/cpufreq.h        | 3 +++
 3 files changed, 15 insertions(+)
drivers/cpufreq/cppc_cpufreq.c +4 -0
index 7e8042efedd1..ad96dfb731ab 100644
@@ -952,6 +952,10 @@ static int __init cppc_cpufreq_init(void)
 	ret = cpufreq_register_driver(&cppc_cpufreq_driver);
 	if (ret)
 		cppc_freq_invariance_exit();
+#ifndef CONFIG_ACPI_CPPC_CPUFREQ_FIE
+	else
+		cpufreq_disable_freq_invariance();
+#endif
 
 	return ret;
 }
drivers/cpufreq/cpufreq.c +8 -0
index a7a69f4d7675..4e79f704a8e7 100644
@@ -66,6 +66,14 @@ bool cpufreq_supports_freq_invariance(void)
 	return static_branch_likely(&cpufreq_freq_invariance);
 }
 
+void cpufreq_disable_freq_invariance(void)
+{
+	cpus_read_lock();
+	static_branch_disable_cpuslocked(&cpufreq_freq_invariance);
+	cpus_read_unlock();
+}
+EXPORT_SYMBOL_GPL(cpufreq_disable_freq_invariance);
+
 /* Flag to suspend/resume CPUFreq governors */
 static bool cpufreq_suspended;
include/linux/cpufreq.h +3 -0
index cc894fc38971..698b8e044e89 100644
@@ -249,6 +249,7 @@ void cpufreq_update_policy(unsigned int cpu);
 void cpufreq_update_limits(unsigned int cpu);
 bool have_governor_per_policy(void);
 bool cpufreq_supports_freq_invariance(void);
+void cpufreq_disable_freq_invariance(void);
 struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
 void cpufreq_enable_fast_switch(struct cpufreq_policy *policy);
 void cpufreq_disable_fast_switch(struct cpufreq_policy *policy);

@@ -280,6 +281,8 @@ static inline bool cpufreq_supports_freq_invariance(void)
 {
 	return false;
 }
+
+static inline void cpufreq_disable_freq_invariance(void) { }
 static inline void disable_cpufreq(void) { }
 static inline void cpufreq_update_limits(unsigned int cpu) { }
 static inline unsigned long cpufreq_get_pressure(int cpu)
Signature · 1 line
2.43.0
reviewer
#1 lore raw
Quoted 9 lines · Penghe Geng

CONFIG_ACPI_CPPC_CPUFREQ_FIE gates CPPC counter-based frequency invariance support. When FIE is disabled, the CPPC driver does not register a frequency scale source, but cpufreq_register_driver() still enables cpufreq_freq_invariance for target/fast-switch drivers.

Disable cpufreq frequency invariance after CPPC driver registration when FIE is disabled. This avoids scheduler behavior mismatch when no invariance updates are provided, which can cause major performance regressions on sensitive platforms.

Hi Penghe,

IIUC, even if CPPC FIE is not there, cpufreq still updates frequency scales in cpufreq_freq_transition_end() and cpufreq_driver_fast_switch(), so the frequency scale number is still somewhat meaningful and the 'cpufreq_freq_invariance' static key reflects that correctly.

Any numbers or evidence of that "performance regressions" so that we can understand the issue better?

Thanks,
Jie

Quoted 13 lines

Export cpufreq_disable_freq_invariance() so modular cppc_cpufreq can call it.

Fixes 1eb5dde674f5 ("cpufreq: CPPC: Add support for frequency invariance")
Cc [email protected]
Signed-off-by Penghe Geng <[email protected]>
---
 drivers/cpufreq/cppc_cpufreq.c | 4 ++++
 drivers/cpufreq/cpufreq.c      | 8 ++++++++
 include/linux/cpufreq.h        | 3 +++
 3 files changed, 15 insertions(+)

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