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 7a5670e2a9c7774a030374e63e1fc69370dec6c9..5c6e63df3f0e499174790fc90d5368e04105024c 100644 (file)
--- 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 c280a39d2cf8c93cde31f84665ed69e808fd7fe8..4e518b2a1b0fa959f1e5e57c088c131aa6212fd3 100644 (file)
--- 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