From: Witold Kręcicki <wpk@culm.net>
Date: Fri, 15 Nov 2019 09:47:08 +0000 (+0100)
Subject: ensure isc_queue_t is aligned to double-cacheline size
X-Git-Tag: v9.15.6~1^2~4
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6718a4ef8b55935d4417e59a2b0e005a82e84747;p=thirdparty%2Fbind9.git

ensure isc_queue_t is aligned to double-cacheline size
---

diff --git a/lib/isc/queue.c b/lib/isc/queue.c
index 17290799067..5072adaaa58 100644
--- a/lib/isc/queue.c
+++ b/lib/isc/queue.c
@@ -22,6 +22,8 @@
 
 #define MAX_THREADS 128
 
+#define ALIGNMENT 128
+
 static uintptr_t nulluintptr = (uintptr_t)NULL;
 
 typedef struct node {
@@ -37,12 +39,13 @@ typedef struct node {
 #define HP_HEAD 0
 
 struct isc_queue {
-	alignas(128) atomic_uintptr_t	head;
-	alignas(128) atomic_uintptr_t	tail;
+	alignas(ALIGNMENT) atomic_uintptr_t	head;
+	alignas(ALIGNMENT) atomic_uintptr_t	tail;
 	isc_mem_t			*mctx;
 	int				max_threads;
 	int				taken;
 	isc_hp_t			*hp;
+	void*				alloced_ptr;
 };
 
 static node_t *
@@ -96,8 +99,17 @@ queue_cas_head(isc_queue_t *queue, node_t *cmp, const node_t *val) {
 
 isc_queue_t *
 isc_queue_new(isc_mem_t *mctx, int max_threads) {
-	isc_queue_t *queue = isc_mem_get(mctx, sizeof(*queue));
-	node_t *sentinel = node_new(mctx, nulluintptr);
+	isc_queue_t *queue = NULL;
+	node_t *sentinel = NULL;
+	void *qbuf = NULL;
+	uintptr_t qptr;
+
+	/*
+	 * A trick to allocate an aligned isc_queue_t structure
+	 */
+	qbuf = isc_mem_get(mctx, sizeof(*queue) + ALIGNMENT);
+	qptr = (uintptr_t) qbuf;
+	queue = (isc_queue_t *) (qptr + (ALIGNMENT - (qptr % ALIGNMENT)));
 
 	if (max_threads == 0) {
 		max_threads = MAX_THREADS;
@@ -105,13 +117,16 @@ isc_queue_new(isc_mem_t *mctx, int max_threads) {
 
 	*queue = (isc_queue_t){
 		.max_threads = max_threads,
+		.alloced_ptr = qbuf,
 	};
 
 	isc_mem_attach(mctx, &queue->mctx);
 
 	queue->hp = isc_hp_new(mctx, 1, node_destroy);
 
+	sentinel = node_new(mctx, nulluintptr);
 	atomic_init(&sentinel->enqidx, 0);
+
 	atomic_init(&queue->head, (uintptr_t)sentinel);
 	atomic_init(&queue->tail, (uintptr_t)sentinel);
 
@@ -205,6 +220,7 @@ isc_queue_dequeue(isc_queue_t *queue) {
 void
 isc_queue_destroy(isc_queue_t *queue) {
 	node_t *last = NULL;
+	void *alloced = NULL;
 
 	REQUIRE(queue != NULL);
 
@@ -215,5 +231,8 @@ isc_queue_destroy(isc_queue_t *queue) {
 	last = (node_t *)atomic_load_relaxed(&queue->head);
 	node_destroy(last);
 	isc_hp_destroy(queue->hp);
-	isc_mem_putanddetach(&queue->mctx, queue, sizeof(*queue));
+
+	alloced = queue->alloced_ptr;
+	isc_mem_putanddetach(&queue->mctx, alloced,
+			     sizeof(*queue) + ALIGNMENT);
 }