[Xen-devel] [PATCH 2/4] x86/mwait_idle: Allow limiting the sub C-state

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

Allow limiting the sub C-state using a new command-line parameter, max_substate.
The limit only applies to the highest legal C-state. For example:
 max_cstate = 1, max_substate = 0 ==> C0, C1 okay, but not C1E
 max_cstate = 1, max_substate = 1 ==> C0, C1 and C1E okay, but not C2
 max_cstate = 2, max_substate = 0 ==> C0, C1, C1E, C2 okay, but not C3
 max_cstate = 2, max_substate = 1 ==> C0, C1, C1E, C2 okay, but not C3

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
 xen/arch/x86/acpi/cpu_idle.c  | 3 +++
 xen/arch/x86/cpu/mwait-idle.c | 4 +++-
 xen/include/xen/acpi.h        | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index b05fb39..96909b3 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -106,6 +106,8 @@ static uint64_t (*__read_mostly tick_to_ns)(uint64_t) = 
acpi_pm_tick_to_ns;
 void (*__read_mostly pm_idle_save)(void);
 unsigned int max_cstate __read_mostly = ACPI_PROCESSOR_MAX_POWER - 1;
 integer_param("max_cstate", max_cstate);
+unsigned int max_substate __read_mostly = ACPI_PROCESSOR_MAX_POWER - 1;
+integer_param("max_substate", max_substate);
 static bool_t __read_mostly local_apic_timer_c2_ok;
 boolean_param("lapic_timer_c2_ok", local_apic_timer_c2_ok);
 
@@ -240,6 +242,7 @@ static void print_acpi_power(uint32_t cpu, struct 
acpi_processor_power *power)
     last_state_idx = power->last_state ? power->last_state->idx : -1;
     printk("active state:\t\tC%d\n", last_state_idx);
     printk("max_cstate:\t\tC%d\n", max_cstate);
+    printk("max_substate:\t\t%d\n", max_substate);
     printk("states:\n");
     
     for ( i = 1; i < power->count; i++ )
diff --git a/xen/arch/x86/cpu/mwait-idle.c b/xen/arch/x86/cpu/mwait-idle.c
index 38172e5..90c8aea 100644
--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -330,7 +330,9 @@ static void mwait_idle(void)
            (next_state = cpuidle_current_governor->select(power)) > 0) {
                do {
                        cx = &power->states[next_state];
-               } while (cx->type > max_cstate && --next_state);
+               } while ((cx->type > max_cstate || (cx->type == max_cstate &&
+                         MWAIT_HINT2SUBSTATE(cx->address) > max_substate)) &&
+                        --next_state);
                if (!next_state)
                        cx = NULL;
                menu_get_trace_data(&exp, &pred);
diff --git a/xen/include/xen/acpi.h b/xen/include/xen/acpi.h
index aedec65..b49c4fc 100644
--- a/xen/include/xen/acpi.h
+++ b/xen/include/xen/acpi.h
@@ -140,6 +140,8 @@ static inline void acpi_set_cstate_limit(unsigned int 
new_limit)
        max_cstate = new_limit;
        return;
 }
+
+extern unsigned int max_substate;
 #else
 static inline unsigned int acpi_get_cstate_limit(void) { return 0; }
 static inline void acpi_set_cstate_limit(unsigned int new_limit) { return; }
-- 
1.9.3


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