[PATCH] cpufreq: acpi: Defer setting boost MSRs

[Stuart Hayes <stuart.w.hayes@gmail.com>]

When acpi-cpufreq is loaded, boost is enabled on every CPU (by setting an
MSR) before the driver is registered with cpufreq.  This can be very time
consuming, because it is done with a CPU hotplug startup callback, and
cpuhp_setup_state() schedules the callback (cpufreq_boost_online()) to run
on each CPU one at a time, waiting for each to run before calling the next.

If cpufreq_register_driver() fails--if, for example, there are no ACPI
P-states present--this is wasted time.

Since cpufreq already sets up a CPU hotplug startup callback if and when
acpi-cpufreq is registered, set the boost MSRs in acpi_cpufreq_cpu_init(),
which is called by the cpufreq cpuhp callback.  This allows acpi-cpufreq to
exit quickly if it is loaded but not needed.

On one system with 192 CPUs, this patch speeds up boot by about 30 seconds.

Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
---
 drivers/cpufreq/acpi-cpufreq.c | 31 +++----------------------------
 1 file changed, 3 insertions(+), 28 deletions(-)

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 1bb2b90ebb21..cb167263de72 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -535,15 +535,6 @@ static void free_acpi_perf_data(void)
 	free_percpu(acpi_perf_data);
 }
 
-static int cpufreq_boost_online(unsigned int cpu)
-{
-	/*
-	 * On the CPU_UP path we simply keep the boost-disable flag
-	 * in sync with the current global state.
-	 */
-	return boost_set_msr(acpi_cpufreq_driver.boost_enabled);
-}
-
 static int cpufreq_boost_down_prep(unsigned int cpu)
 {
 	/*
@@ -897,6 +888,8 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	if (perf->states[0].core_frequency * 1000 != freq_table[0].frequency)
 		pr_warn(FW_WARN "P-state 0 is not max freq\n");
 
+	set_boost(policy, acpi_cpufreq_driver.boost_enabled);
+
 	return result;
 
 err_unreg:
@@ -916,6 +909,7 @@ static int acpi_cpufreq_cpu_exit(struct cpufreq_policy *policy)
 
 	pr_debug("%s\n", __func__);
 
+	cpufreq_boost_down_prep(policy->cpu);
 	policy->fast_switch_possible = false;
 	policy->driver_data = NULL;
 	acpi_processor_unregister_performance(data->acpi_perf_cpu);
@@ -972,25 +966,9 @@ static void __init acpi_cpufreq_boost_init(void)
 	acpi_cpufreq_driver.set_boost = set_boost;
 	acpi_cpufreq_driver.boost_enabled = boost_state(0);
 
-	/*
-	 * This calls the online callback on all online cpu and forces all
-	 * MSRs to the same value.
-	 */
-	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "cpufreq/acpi:online",
-				cpufreq_boost_online, cpufreq_boost_down_prep);
-	if (ret < 0) {
-		pr_err("acpi_cpufreq: failed to register hotplug callbacks\n");
-		return;
-	}
 	acpi_cpufreq_online = ret;
 }
 
-static void acpi_cpufreq_boost_exit(void)
-{
-	if (acpi_cpufreq_online > 0)
-		cpuhp_remove_state_nocalls(acpi_cpufreq_online);
-}
-
 static int __init acpi_cpufreq_init(void)
 {
 	int ret;
@@ -1032,7 +1010,6 @@ static int __init acpi_cpufreq_init(void)
 	ret = cpufreq_register_driver(&acpi_cpufreq_driver);
 	if (ret) {
 		free_acpi_perf_data();
-		acpi_cpufreq_boost_exit();
 	}
 	return ret;
 }
@@ -1041,8 +1018,6 @@ static void __exit acpi_cpufreq_exit(void)
 {
 	pr_debug("%s\n", __func__);
 
-	acpi_cpufreq_boost_exit();
-
 	cpufreq_unregister_driver(&acpi_cpufreq_driver);
 
 	free_acpi_perf_data();
-- 
2.31.1