From: Avi Kivity <avi@redhat.com>
Date: Tue, 26 Jul 2011 11:26:13 +0000 (+0300)
Subject: memory: transaction API
X-Git-Tag: qemu-xen-4.3.0-rc1~2628^2~82
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=4ef4db860362ce9852c20b343e9813897ecdefce;p=qemu-upstream-4.5-testing.git

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>
---

diff --git a/memory.c b/memory.c
index 7a5670e2a..5c6e63df3 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 c280a39d2..4e518b2a1 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