[v5,7/7] target-i386/kvm: cache the return value of kvm_enable_x2apic()

Commit Message

Radim Krčmář Oct. 10, 2016, 3:28 p.m. UTC

Assume that KVM would have returned the same on subsequent runs.
Abstract the memoizaiton pattern into macros and call it memorize as
adding the r makes it less obscure.

Reviewed-by: Igor Mammedov <[e-mail]>
Signed-off-by: Radim Krčmář <[e-mail]>
---
v5: r-b Igor
v4:
 * changed the name to memorize [Igor]
 * remove useless underscores in macro arguments
 * merge the two macros, as it seems that the deleted one wouldn't get
   other users anytime soon
---
 target-i386/kvm.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

Patch

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 0fd664648665..0472f45fd092 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -129,10 +129,23 @@  static bool kvm_x2apic_api_set_flags(uint64_t flags)
     return !kvm_vm_enable_cap(s, KVM_CAP_X2APIC_API, 0, flags);
 }
 
+#define MEMORIZE(fn) \
+    ({ \
+        static typeof(fn) _result; \
+        static bool _memorized; \
+        \
+        if (_memorized) { \
+            return _result; \
+        } \
+        _memorized = true; \
+        _result = fn; \
+    })
+
 bool kvm_enable_x2apic(void)
 {
-    return kvm_x2apic_api_set_flags(KVM_X2APIC_API_USE_32BIT_IDS |
-                                    KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK);
+    return MEMORIZE(
+             kvm_x2apic_api_set_flags(KVM_X2APIC_API_USE_32BIT_IDS |
+                                      KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK));
 }
 
 static int kvm_get_tsc(CPUState *cs)