[Qemu-devel] [PATCH v2 14/23] memory: transaction API

[Avi Kivity]

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 <address@hidden>
---
 memory.c |   18 ++++++++++++++++++
 memory.h |    8 ++++++++
 2 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/memory.c b/memory.c
index 7a5670e..5c6e63d 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 c280a39..4e518b2 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
-- 
1.7.5.3