[Qemu-devel] [PATCH v4 2/2] QOM: object_property_add() performance improvement

[Pavel Fedin]

Avoid repetitive lookup of every property in array starting from 0 by adding
one more property which caches last used index. Every time an array is
expanded the index is picked up from this cache.

The property is a uint32_t and its name is name of the array plus '#'
('name#'). It has getter function in order to allow to inspect it from
within monitor.

Another optimization includes avoiding reallocation of 'full_name' every
iteration. Instead, name_no_array buffer is extended and reused.

Signed-off-by: Pavel Fedin <address@hidden>
Reviewed-by: Peter Crosthwaite <address@hidden>
---
 qom/object.c | 51 ++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 40 insertions(+), 11 deletions(-)

diff --git a/qom/object.c b/qom/object.c
index ba63777..5820df2 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -10,6 +10,8 @@
  * See the COPYING file in the top-level directory.
  */
 
+#include <glib/gprintf.h>
+
 #include "qom/object.h"
 #include "qom/object_interfaces.h"
 #include "qemu-common.h"
@@ -862,6 +864,14 @@ object_property_add_single(Object *obj, const char *name, 
const char *type,
     return prop;
 }
 
+static void
+property_get_uint32_opaque(Object *obj, Visitor *v, void *opaque,
+                           const char *name, Error **errp)
+{
+    uint32_t value = (uintptr_t)opaque;
+    visit_type_uint32(v, &value, name, errp);
+}
+
 ObjectProperty *
 object_property_add(Object *obj, const char *name, const char *type,
                     ObjectPropertyAccessor *get,
@@ -871,27 +881,46 @@ object_property_add(Object *obj, const char *name, const 
char *type,
 {
     size_t name_len = strlen(name);
     char *name_no_array;
-    ObjectProperty *ret;
-    int i;
+    ObjectProperty *ret, *count;
+    uintptr_t i;
 
     if (name_len < 3 || memcmp(&name[name_len - 3], "[*]", 4)) {
         return object_property_add_single(obj, name, type,
                                           get, set, release, opaque, errp);
     }
 
-    name_no_array = g_strdup(name);
-
-    name_no_array[name_len - 3] = '\0';
-    for (i = 0; ; ++i) {
-        char *full_name = g_strdup_printf("%s[%d]", name_no_array, i);
-
-        ret = object_property_add(obj, full_name, type, get, set,
-                                  release, opaque, NULL);
-        g_free(full_name);
+    /* 20 characters for maximum possible uintptr_t (64-bit) */
+    name_no_array = g_malloc(name_len + 20);
+    name_len -= 3;
+    memcpy(name_no_array, name, name_len);
+
+    name_no_array[name_len] = '#';
+    name_no_array[name_len + 1] = '\0';
+    count = object_property_find(obj, name_no_array, NULL);
+    if (count == NULL) {
+        /* This is very similar to object_property_add_uint32_ptr(), but:
+         * - Returns pointer
+         * - Will not recurse here, avoiding one condition check
+         * - Allows us to use 'opaque' pointer itself as a storage, because
+         *   we want to store only a single integer which should never be
+         *   modified from outside.
+         */
+        count = object_property_add_single(obj, name_no_array, "uint32",
+                                           property_get_uint32_opaque, NULL,
+                                           NULL, NULL, &error_abort);
+    }
+
+    for (i = (uintptr_t)count->opaque; ; ++i) {
+        g_sprintf(&name_no_array[name_len], "[%zu]", i);
+
+        ret = object_property_add_single(obj, name_no_array, type, get, set,
+                                         release, opaque, NULL);
         if (ret) {
             break;
         }
     }
+
+    count->opaque = (void *)i;
     g_free(name_no_array);
     return ret;
 }
-- 
1.9.5.msysgit.0