[v2,2/5] x86/cpuidle: really use C1 for "urgent" CPUs

Commit Message

Jan Beulich July 3, 2019, 1 p.m. UTC

For one on recent AMD CPUs entering C1 (if available at all) requires
use of MWAIT, while HLT (i.e. default_idle()) would put the processor
into as deep as CC6. And then even on other vendors' CPUs we should
avoid entering default_idle() when the intended state can be reached
by using the active idle driver's facilities.

Signed-off-by: Jan Beulich <[e-mail]>
Reviewed-by: Andrew Cooper <[e-mail]>

Patch

--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -582,12 +582,15 @@  static void acpi_processor_idle(void)
      u32 exp = 0, pred = 0;
      u32 irq_traced[4] = { 0 };
  
-    if ( max_cstate > 0 && power && !sched_has_urgent_vcpu() &&
+    if ( max_cstate > 0 && power &&
           (next_state = cpuidle_current_governor->select(power)) > 0 )
      {
+        unsigned int max_state = sched_has_urgent_vcpu() ? ACPI_STATE_C1
+                                                         : max_cstate;
+
          do {
              cx = &power->states[next_state];
-        } while ( cx->type > max_cstate && --next_state );
+        } while ( cx->type > max_state && --next_state );
          if ( next_state )
          {
              if ( cx->type == ACPI_STATE_C3 && power->flags.bm_check &&
--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -724,11 +724,14 @@  static void mwait_idle(void)
  	u64 before, after;
  	u32 exp = 0, pred = 0, irq_traced[4] = { 0 };
  
-	if (max_cstate > 0 && power && !sched_has_urgent_vcpu() &&
+	if (max_cstate > 0 && power &&
  	    (next_state = cpuidle_current_governor->select(power)) > 0) {
+		unsigned int max_state = sched_has_urgent_vcpu() ? ACPI_STATE_C1
+								 : max_cstate;
+
  		do {
  			cx = &power->states[next_state];
-		} while (cx->type > max_cstate && --next_state);
+		} while (cx->type > max_state && --next_state);
  		if (!next_state)
  			cx = NULL;
  		else if (tb_init_done)