From: Remi Tricot-Le Breton <rlebreton@haproxy.com>
Date: Thu, 16 Nov 2023 16:38:12 +0000 (+0100)
Subject: MEDIUM: shctx: Move list between hot and avail list in O(1)
X-Git-Tag: v2.9-dev10~63
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=eccb97f60e4b47b2511177b23dced6aadb7419da;p=thirdparty%2Fhaproxy.git

MEDIUM: shctx: Move list between hot and avail list in O(1)

Instead of iterating over all the elements of a given row when moving it
between the hot and available lists, we can make use of the last_reserved
pointer that already points to the last block of the list to perform the
move in O(1).
---

diff --git a/src/shctx.c b/src/shctx.c
index 862adb68ba..19394fa175 100644
--- a/src/shctx.c
+++ b/src/shctx.c
@@ -145,21 +145,21 @@ out:
  */
 void shctx_row_inc_hot(struct shared_context *shctx, struct shared_block *first)
 {
-	struct shared_block *block, *sblock;
-	int count = 0;
-
 	if (first->refcount <= 0) {
 
-		block = first;
+		BUG_ON(!first->last_reserved);
 
-		list_for_each_entry_safe_from(block, sblock, &shctx->avail, list) {
+		/* Detach row from avail list, link first item's prev to last
+		 * item's next. This allows to use the LIST_SPLICE_END_DETACHED
+		 * macro. */
+		first->list.p->n = first->last_reserved->list.n;
+		first->last_reserved->list.n->p = first->list.p;
 
-			shctx_block_set_hot(shctx, block);
+		/* Reattach to hot list */
+		first->list.p = &first->last_reserved->list;
+		LIST_SPLICE_END_DETACHED(&shctx->hot, &first->list);
 
-			count++;
-			if (count >= first->block_count)
-				break;
-		}
+		shctx->nbav -= first->block_count;
 	}
 
 	first->refcount++;
@@ -170,25 +170,24 @@ void shctx_row_inc_hot(struct shared_context *shctx, struct shared_block *first)
  */
 void shctx_row_dec_hot(struct shared_context *shctx, struct shared_block *first)
 {
-	struct shared_block *block, *sblock;
-	int count = 0;
-
 	first->refcount--;
 
 	if (first->refcount <= 0) {
 
-		block = first;
+		BUG_ON(!first->last_reserved);
 
-		list_for_each_entry_safe_from(block, sblock, &shctx->hot, list) {
+		/* Detach row from hot list, link first item's prev to last
+		 * item's next. This allows to use the LIST_SPLICE_END_DETACHED
+		 * macro. */
+		first->list.p->n = first->last_reserved->list.n;
+		first->last_reserved->list.n->p = first->list.p;
 
-			shctx_block_set_avail(shctx, block);
+		/* Reattach to avail list */
+		first->list.p = &first->last_reserved->list;
+		LIST_SPLICE_END_DETACHED(&shctx->avail, &first->list);
 
-			count++;
-			if (count >= first->block_count)
-				break;
-		}
+		shctx->nbav += first->block_count;
 	}
-
 }