x86: Use deep C states for off-lined CPUs

Currently when a core is taken off-line it is placed in C1 state (unless
MONITOR/MWAIT is used). This patch allows a core to go to deeper C states
resulting in significantly higher power savings.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@amd.com>
Committed-by: Jan Beulich <jbeulich@suse.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index 0102b6329e..90168548bc 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -602,6 +602,23 @@ static void acpi_dead_idle(void)
             __mwait(cx->address, 0);
         }
     }
+    else if ( current_cpu_data.x86_vendor == X86_VENDOR_AMD &&
+              cx->entry_method == ACPI_CSTATE_EM_SYSIO )
+    {
+        /* Intel prefers not to use SYSIO */
+
+        /* Avoid references to shared data after the cache flush */
+        u32 address = cx->address;
+        u32 pmtmr_ioport_local = pmtmr_ioport;
+
+        wbinvd();
+
+        while ( 1 )
+        {
+            inb(address);
+            inl(pmtmr_ioport_local);
+        }
+    }
 
 default_halt:
     for ( ; ; )