From 4ef4db860362ce9852c20b343e9813897ecdefce Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@redhat.com>
Date: Tue, 26 Jul 2011 14:26:13 +0300
Subject: [PATCH] memory: transaction API

Allow changes to the memory hierarchy to be accumulated and
made visible all at once.  This reduces computational effort,
especially when an accelerator (e.g. kvm) is involved.

Useful when a single register update causes multiple changes
to an address space.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
 memory.c | 18 ++++++++++++++++++
 memory.h |  8 ++++++++
 2 files changed, 26 insertions(+)

diff --git a/memory.c b/memory.c
index 7a5670e2a9..5c6e63df3f 100644
--- a/memory.c
+++ b/memory.c
@@ -18,6 +18,8 @@
 #include "kvm.h"
 #include <assert.h>
 
+unsigned memory_region_transaction_depth = 0;
+
 typedef struct AddrRange AddrRange;
 
 struct AddrRange {
@@ -626,6 +628,10 @@ static void address_space_update_topology(AddressSpace *as)
 
 static void memory_region_update_topology(void)
 {
+    if (memory_region_transaction_depth) {
+        return;
+    }
+
     if (address_space_memory.root) {
         address_space_update_topology(&address_space_memory);
     }
@@ -634,6 +640,18 @@ static void memory_region_update_topology(void)
     }
 }
 
+void memory_region_transaction_begin(void)
+{
+    ++memory_region_transaction_depth;
+}
+
+void memory_region_transaction_commit(void)
+{
+    assert(memory_region_transaction_depth);
+    --memory_region_transaction_depth;
+    memory_region_update_topology();
+}
+
 void memory_region_init(MemoryRegion *mr,
                         const char *name,
                         uint64_t size)
diff --git a/memory.h b/memory.h
index c280a39d2c..4e518b2a1b 100644
--- a/memory.h
+++ b/memory.h
@@ -456,6 +456,14 @@ void memory_region_add_subregion_overlap(MemoryRegion *mr,
 void memory_region_del_subregion(MemoryRegion *mr,
                                  MemoryRegion *subregion);
 
+/* Start a transaction; changes will be accumulated and made visible only
+ * when the transaction ends.
+ */
+void memory_region_transaction_begin(void);
+/* Commit a transaction and make changes visible to the guest.
+ */
+void memory_region_transaction_commit(void);
+
 #endif
 
 #endif