[Xen-devel] [PATCH v2 2/3] x86/cpuidle: push parked CPUs into deeper sleep states when possible

["Jan Beulich" <JBeulich@xxxxxxxx>]

When the mwait-idle driver isn't used, C-state information becomes
available only in the course of Dom0 starting up. Use the provided data
to allow parked CPUs to sleep in a more energy efficient way, by waking
them briefly (via NMI) once the data has been recorded.

This involves re-arranging how/when the governor's ->enable() hook gets
invoked. The changes there include addition of so far missing error
handling in the respective CPU notifier handlers.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -351,12 +351,22 @@ static void dump_cx(unsigned char key)
     unsigned int cpu;
 
     printk("'%c' pressed -> printing ACPI Cx structures\n", key);
-    for_each_online_cpu ( cpu )
-        if (processor_powers[cpu])
-        {
-            print_acpi_power(cpu, processor_powers[cpu]);
-            process_pending_softirqs();
-        }
+    for_each_present_cpu ( cpu )
+    {
+        struct acpi_processor_power *power = processor_powers[cpu];
+
+        if ( !power )
+            continue;
+
+        if ( cpu_online(cpu) )
+            print_acpi_power(cpu, power);
+        else if ( park_offline_cpus )
+            printk("CPU%u parked in state %u (C%u)\n", cpu,
+                   power->last_state ? power->last_state->idx : 1,
+                   power->last_state ? power->last_state->type : 1);
+
+        process_pending_softirqs();
+    }
 }
 
 static int __init cpu_idle_key_init(void)
@@ -765,6 +775,7 @@ void acpi_dead_idle(void)
         goto default_halt;
 
     cx = &power->states[power->count - 1];
+    power->last_state = cx;
 
     if ( cx->entry_method == ACPI_CSTATE_EM_FFH )
     {
@@ -1217,9 +1228,30 @@ long set_cx_pminfo(uint32_t acpi_id, str
         set_cx(acpi_power, &xen_cx);
     }
 
-    if ( cpuidle_current_governor->enable &&
-         cpuidle_current_governor->enable(acpi_power) )
-        return -EFAULT;
+    if ( !cpu_online(cpu_id) )
+    {
+        uint32_t apic_id = x86_cpu_to_apicid[cpu_id];
+
+        /*
+         * If we've just learned of more available C states, wake the CPU if
+         * it's parked, so it can go back to sleep in perhaps a deeper state.
+         */
+        if ( park_offline_cpus && apic_id != BAD_APICID )
+        {
+            unsigned long flags;
+
+            local_irq_save(flags);
+            apic_wait_icr_idle();
+            apic_icr_write(APIC_DM_NMI | APIC_DEST_PHYSICAL, apic_id);
+            local_irq_restore(flags);
+        }
+    }
+    else if ( cpuidle_current_governor->enable )
+    {
+        ret = cpuidle_current_governor->enable(acpi_power);
+        if ( ret < 0 )
+            return ret;
+    }
 
     /* FIXME: C-state dependency is not supported by far */
 
@@ -1379,19 +1411,22 @@ static int cpu_callback(
     struct notifier_block *nfb, unsigned long action, void *hcpu)
 {
     unsigned int cpu = (unsigned long)hcpu;
+    int rc = 0;
 
-    /* Only hook on CPU_ONLINE because a dead cpu may utilize the info to
-     * to enter deep C-state */
+    /*
+     * Only hook on CPU_UP_PREPARE because a dead cpu may utilize the info
+     * to enter deep C-state.
+     */
     switch ( action )
     {
-    case CPU_ONLINE:
-        (void)cpuidle_init_cpu(cpu);
-        break;
-    default:
+    case CPU_UP_PREPARE:
+        rc = cpuidle_init_cpu(cpu);
+        if ( !rc && cpuidle_current_governor->enable )
+            rc = cpuidle_current_governor->enable(processor_powers[cpu]);
         break;
     }
 
-    return NOTIFY_DONE;
+    return !rc ? NOTIFY_DONE : notifier_from_errno(rc);
 }
 
 static struct notifier_block cpu_nfb = {
@@ -1406,6 +1441,7 @@ static int __init cpuidle_presmp_init(vo
         return 0;
 
     mwait_idle_init(&cpu_nfb);
+    cpu_nfb.notifier_call(&cpu_nfb, CPU_UP_PREPARE, cpu);
     cpu_nfb.notifier_call(&cpu_nfb, CPU_ONLINE, cpu);
     register_cpu_notifier(&cpu_nfb);
     return 0;
--- a/xen/arch/x86/acpi/cpuidle_menu.c
+++ b/xen/arch/x86/acpi/cpuidle_menu.c
@@ -277,9 +277,6 @@ static void menu_reflect(struct acpi_pro
 
 static int menu_enable_device(struct acpi_processor_power *power)
 {
-    if (!cpu_online(power->cpu))
-        return -1;
-
     memset(&per_cpu(menu_devices, power->cpu), 0, sizeof(struct menu_device));
 
     return 0;
--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -1166,12 +1166,17 @@ static int mwait_idle_cpu_init(struct no
        struct acpi_processor_power *dev = processor_powers[cpu];
 
        switch (action) {
+               int rc;
+
        default:
                return NOTIFY_DONE;
 
        case CPU_UP_PREPARE:
-               cpuidle_init_cpu(cpu);
-               return NOTIFY_DONE;
+               rc = cpuidle_init_cpu(cpu);
+               dev = processor_powers[cpu];
+               if (!rc && cpuidle_current_governor->enable)
+                       rc = cpuidle_current_governor->enable(dev);
+               return !rc ? NOTIFY_DONE : notifier_from_errno(rc);
 
        case CPU_ONLINE:
                if (!dev)
@@ -1260,8 +1265,6 @@ int __init mwait_idle_init(struct notifi
        }
        if (!err) {
                nfb->notifier_call = mwait_idle_cpu_init;
-               mwait_idle_cpu_init(nfb, CPU_UP_PREPARE, NULL);
-
                pm_idle_save = pm_idle;
                pm_idle = mwait_idle;
                dead_idle = acpi_dead_idle;




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