From: alessio <alessio@isc.org>
Date: Thu, 30 Jan 2025 11:33:48 +0000 (+0100)
Subject: Remove zero initialization of large buffers
X-Git-Tag: v9.21.7~4^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4017a40b1de475ca52fe0f5488d0045367cf31a5;p=thirdparty%2Fbind9.git

Remove zero initialization of large buffers

Profiles show that an high amount of CPU time spent in memset.
By removing zero initalization of certain large buffers we improve
performance in certain authoritative workloads.
---

diff --git a/lib/dns/qp.c b/lib/dns/qp.c
index 3805845b914..79a0b8e6eeb 100644
--- a/lib/dns/qp.c
+++ b/lib/dns/qp.c
@@ -1785,10 +1785,14 @@ dns_qpchain_init(dns_qpreadable_t qpr, dns_qpchain_t *chain) {
 	REQUIRE(QP_VALID(qp));
 	REQUIRE(chain != NULL);
 
-	*chain = (dns_qpchain_t){
-		.magic = QPCHAIN_MAGIC,
-		.qp = qp,
-	};
+	/*
+	 * dns_qpchain_t contains a 2kb buffer, which is slow to
+	 * zero-initialize. Therefore we avoid designated initializers, and
+	 * initialize each field manually.
+	 */
+	chain->magic = QPCHAIN_MAGIC;
+	chain->qp = qp;
+	chain->len = 0;
 }
 
 unsigned int
@@ -1821,10 +1825,19 @@ dns_qpiter_init(dns_qpreadable_t qpr, dns_qpiter_t *qpi) {
 	dns_qpreader_t *qp = dns_qpreader(qpr);
 	REQUIRE(QP_VALID(qp));
 	REQUIRE(qpi != NULL);
-	*qpi = (dns_qpiter_t){
-		.qp = qp,
-		.magic = QPITER_MAGIC,
-	};
+
+	/*
+	 * dns_qpiter_t contains a 4kb buffer, which is slow to zero-initialize.
+	 * Therefore we avoid designated initializers, and initialize each
+	 * field manually.
+	 */
+	qpi->qp = qp;
+	qpi->sp = 0;
+	qpi->magic = QPITER_MAGIC;
+	/*
+	 * The top of the stack must be initialized.
+	 */
+	qpi->stack[qpi->sp] = NULL;
 }
 
 /*
diff --git a/lib/dns/qpcache.c b/lib/dns/qpcache.c
index 1b506082039..3b7f5680b1d 100644
--- a/lib/dns/qpcache.c
+++ b/lib/dns/qpcache.c
@@ -1458,6 +1458,29 @@ find_coveringnsec(qpc_search_t *search, const dns_name_t *name,
 	 (DNS_TRUST_PENDING((found)->trust) &&             \
 	  (((options) & DNS_DBFIND_PENDINGOK) == 0)))
 
+static void
+qpc_search_init(qpc_search_t *search, qpcache_t *db, unsigned int options,
+		isc_stdtime_t now) {
+	/*
+	 * qpc_search_t contains two structures with large buffers (dns_qpiter_t
+	 * and dns_qpchain_t). Those two structures will be initialized later by
+	 * dns_qp_lookup anyway.
+	 * To avoid the overhead of zero initialization, we avoid designated
+	 * initializers and initialize all "small" fields manually.
+	 */
+	search->qpdb = (qpcache_t *)db;
+	search->options = options;
+	/*
+	 * qpch->in - Init by dns_qp_lookup
+	 * qpiter - Init by dns_qp_lookup
+	 */
+	search->need_cleanup = false;
+	search->now = now ? now : isc_stdtime_now();
+	search->zonecut = NULL;
+	search->zonecut_header = NULL;
+	search->zonecut_sigheader = NULL;
+}
+
 static isc_result_t
 qpcache_find(dns_db_t *db, const dns_name_t *name, dns_dbversion_t *version,
 	     dns_rdatatype_t type, unsigned int options, isc_stdtime_t __now,
@@ -1479,11 +1502,9 @@ qpcache_find(dns_db_t *db, const dns_name_t *name, dns_dbversion_t *version,
 	dns_slabheader_t *foundsig = NULL, *nssig = NULL, *cnamesig = NULL;
 	dns_slabheader_t *nsecheader = NULL, *nsecsig = NULL;
 	dns_typepair_t sigtype, negtype;
-	qpc_search_t search = (qpc_search_t){
-		.qpdb = (qpcache_t *)db,
-		.options = options,
-		.now = __now ? __now : isc_stdtime_now(),
-	};
+
+	qpc_search_t search;
+	qpc_search_init(&search, (qpcache_t *)db, options, __now);
 
 	REQUIRE(VALID_QPDB((qpcache_t *)db));
 	REQUIRE(version == NULL);
diff --git a/lib/dns/qpzone.c b/lib/dns/qpzone.c
index 9ede2dfa4ce..4c60d4c17d0 100644
--- a/lib/dns/qpzone.c
+++ b/lib/dns/qpzone.c
@@ -3326,6 +3326,34 @@ qpzone_check_zonecut(qpznode_t *node, void *arg DNS__DB_FLARG) {
 	return result;
 }
 
+static void
+qpz_search_init(qpz_search_t *search, qpzonedb_t *db, qpz_version_t *version,
+		unsigned int options) {
+	/*
+	 * qpz_search_t contains two structures with large buffers (dns_qpiter_t
+	 * and dns_qpchain_t). Those two structures will be initialized later by
+	 * dns_qp_lookup anyway.
+	 * To avoid the overhead of zero initialization, we avoid designated
+	 * initializers and initialize all "small" fields manually.
+	 */
+	search->qpdb = db;
+	search->version = version;
+	search->qpr = (dns_qpread_t){};
+	search->serial = version->serial;
+	search->options = options;
+	/*
+	 * qpch->in -- init in dns_qp_lookup
+	 * qpiter -- init in dns_qp_lookup
+	 */
+	search->copy_name = false;
+	search->need_cleanup = false;
+	search->wild = false;
+	search->zonecut = NULL;
+	search->zonecut_header = NULL;
+	search->zonecut_sigheader = NULL;
+	dns_fixedname_init(&search->zonecut_name);
+}
+
 static isc_result_t
 qpzone_find(dns_db_t *db, const dns_name_t *name, dns_dbversion_t *version,
 	    dns_rdatatype_t type, unsigned int options,
@@ -3335,7 +3363,6 @@ qpzone_find(dns_db_t *db, const dns_name_t *name, dns_dbversion_t *version,
 	isc_result_t result;
 	qpzonedb_t *qpdb = (qpzonedb_t *)db;
 	qpznode_t *node = NULL;
-	qpz_search_t search;
 	bool cname_ok = true, close_version = false;
 	bool maybe_zonecut = false, at_zonecut = false;
 	bool wild = false, empty_node = false;
@@ -3361,13 +3388,9 @@ qpzone_find(dns_db_t *db, const dns_name_t *name, dns_dbversion_t *version,
 		close_version = true;
 	}
 
-	search = (qpz_search_t){
-		.qpdb = (qpzonedb_t *)db,
-		.version = (qpz_version_t *)version,
-		.serial = ((qpz_version_t *)version)->serial,
-		.options = options,
-	};
-	dns_fixedname_init(&search.zonecut_name);
+	qpz_search_t search;
+	qpz_search_init(&search, (qpzonedb_t *)db, (qpz_version_t *)version,
+			options);
 
 	if ((options & DNS_DBFIND_FORCENSEC3) != 0) {
 		dns_qpmulti_query(qpdb->nsec3, &search.qpr);