Try to skip lock on fully lower names

If the name is fully lowercase, we don't need to access the case bitmap
in order to set the case. Therefore, we can check for the FULLYLOWERCASE
flag using only atomic operations, and skip a lock in the hot path,
provided we clear the FULLYLOWERCASE flag before changing the case
bitmap.

diff --git a/lib/dns/rdataslab.c b/lib/dns/rdataslab.c
index e7c5539458ed2514df32dd45ae2991377fbd7e16..8b158a15c022b60cc493eae6074e2606962befd1 100644 (file)
--- a/lib/dns/rdataslab.c
+++ b/lib/dns/rdataslab.c
@@ -870,7 +870,7 @@ dns_slabheader_reset(dns_slabheader_t *h, dns_db_t *db, dns_dbnode_t *node) {
        atomic_init(&h->attributes, 0);
        atomic_init(&h->last_refresh_fail_ts, 0);
 
-       STATIC_ASSERT((sizeof(h->attributes) == 2),
+       STATIC_ASSERT(sizeof(h->attributes) == 2,
                      "The .attributes field of dns_slabheader_t needs to be "
                      "16-bit int type exactly.");
 }
@@ -1208,6 +1208,8 @@ static void
 rdataset_setownercase(dns_rdataset_t *rdataset, const dns_name_t *name) {
        dns_slabheader_t *header = dns_rdataset_getheader(rdataset);
 
+       DNS_SLABHEADER_CLRATTR(header, DNS_SLABHEADERATTR_CASEFULLYLOWER);
+
        dns_db_locknode(header->db, header->node, isc_rwlocktype_write);
        dns_slabheader_setownercase(header, name);
        dns_db_unlocknode(header->db, header->node, isc_rwlocktype_write);
@@ -1219,15 +1221,13 @@ rdataset_getownercase(const dns_rdataset_t *rdataset, dns_name_t *name) {
        uint8_t mask = (1 << 7);
        uint8_t bits = 0;
 
-       dns_db_locknode(header->db, header->node, isc_rwlocktype_read);
-
-       if (!CASESET(header)) {
-               goto unlock;
-       }
-
        if (CASEFULLYLOWER(header)) {
                isc_ascii_lowercopy(name->ndata, name->ndata, name->length);
-       } else {
+               return;
+       }
+
+       dns_db_locknode(header->db, header->node, isc_rwlocktype_read);
+       if (CASESET(header)) {
                uint8_t *nd = name->ndata;
                for (size_t i = 0; i < name->length; i++) {
                        if (mask == (1 << 7)) {
@@ -1240,8 +1240,6 @@ rdataset_getownercase(const dns_rdataset_t *rdataset, dns_name_t *name) {
                                              : isc_ascii_tolower(nd[i]);
                }
        }
-
-unlock:
        dns_db_unlocknode(header->db, header->node, isc_rwlocktype_read);
 }