commit e08cc001d502958040565636e19a42c06e1ae8b7
author Emanuele Giuseppe Esposito <eesposit@redhat.com> Tue Oct 25 04:49:45 2022 -0400
committer Kevin Wolf <kwolf@redhat.com> Thu Oct 27 20:14:11 2022 +0200
tree d775af529b1d7d598993d80c95ad1a30907d6a47
parent 7e8c182fb5e5950a52623b0d463c2f1fcd15a80a

bdrv_change_aio_context: use hash table instead of list of visited nodes

Minor performance improvement, but given that we have hash tables
available, avoid iterating in the visited nodes list every time just
to check if a node has been already visited.

The data structure is not actually a proper hash map, but an hash set,
as we are just adding nodes and not key,value pairs.

Suggested-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20221025084952.2139888-4-eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

diff --git a/block.c b/block.c
index 38e5d83..59319d9 100644
--- a/block.c
+++ b/block.c
@@ -105,7 +105,7 @@
 static bool bdrv_backing_overridden(BlockDriverState *bs);
 
 static bool bdrv_change_aio_context(BlockDriverState *bs, AioContext *ctx,
-                                    GSList **visited, Transaction *tran,
+                                    GHashTable *visited, Transaction *tran,
                                     Error **errp);
 
 /* If non-zero, use only whitelisted block drivers */
@@ -7315,14 +7315,15 @@
 } BdrvStateSetAioContext;
 
 static bool bdrv_parent_change_aio_context(BdrvChild *c, AioContext *ctx,
-                                           GSList **visited, Transaction *tran,
+                                           GHashTable *visited,
+                                           Transaction *tran,
                                            Error **errp)
 {
     GLOBAL_STATE_CODE();
-    if (g_slist_find(*visited, c)) {
+    if (g_hash_table_contains(visited, c)) {
         return true;
     }
-    *visited = g_slist_prepend(*visited, c);
+    g_hash_table_add(visited, c);
 
     /*
      * A BdrvChildClass that doesn't handle AioContext changes cannot
@@ -7353,14 +7354,14 @@
 }
 
 bool bdrv_child_change_aio_context(BdrvChild *c, AioContext *ctx,
-                                   GSList **visited, Transaction *tran,
+                                   GHashTable *visited, Transaction *tran,
                                    Error **errp)
 {
     GLOBAL_STATE_CODE();
-    if (g_slist_find(*visited, c)) {
+    if (g_hash_table_contains(visited, c)) {
         return true;
     }
-    *visited = g_slist_prepend(*visited, c);
+    g_hash_table_add(visited, c);
     return bdrv_change_aio_context(c->bs, ctx, visited, tran, errp);
 }
 
@@ -7445,7 +7446,7 @@
  * responsible for freeing the list afterwards.
  */
 static bool bdrv_change_aio_context(BlockDriverState *bs, AioContext *ctx,
-                                    GSList **visited, Transaction *tran,
+                                    GHashTable *visited, Transaction *tran,
                                     Error **errp)
 {
     BdrvChild *c;
@@ -7524,7 +7525,7 @@
                                       BdrvChild *ignore_child, Error **errp)
 {
     Transaction *tran;
-    GSList *visited;
+    GHashTable *visited;
     int ret;
     AioContext *old_context = bdrv_get_aio_context(bs);
     GLOBAL_STATE_CODE();
@@ -7536,9 +7537,12 @@
      * is successful (the transaction itself).
      */
     tran = tran_new();
-    visited = ignore_child ? g_slist_prepend(NULL, ignore_child) : NULL;
-    ret = bdrv_change_aio_context(bs, ctx, &visited, tran, errp);
-    g_slist_free(visited);
+    visited = g_hash_table_new(NULL, NULL);
+    if (ignore_child) {
+        g_hash_table_add(visited, ignore_child);
+    }
+    ret = bdrv_change_aio_context(bs, ctx, visited, tran, errp);
+    g_hash_table_destroy(visited);
 
     /*
      * Linear phase: go through all callbacks collected in the transaction.