Cluster: Optimize slot bitmap iteration from per-bit to 64-bit word scan

src/cluster.h

@@ -8,6 +8,7 @@
 
 #define CLUSTER_SLOT_MASK_BITS 14                   /* Number of bits used for slot id. */
 #define CLUSTER_SLOTS (1 << CLUSTER_SLOT_MASK_BITS) /* Total number of slots in cluster mode, which is 16384. */
+#define CLUSTER_SLOT_WORDS (CLUSTER_SLOTS / 64)     /* Treating slot bitmaps as 8-byte words */
 #define CLUSTER_OK 0                                /* Everything looks ok */
 #define CLUSTER_FAIL 1                              /* The cluster can't work */
 #define CLUSTER_NAMELEN 40                          /* sha1 hex length */

src/cluster_legacy.c

@@ -4105,20 +4105,30 @@ int clusterProcessPacket(clusterLink *link) {
              * new configuration, so other nodes that have an updated table must
              * do it. In this way A will stop to act as a primary (or can try to
              * failover if there are the conditions to win the election). */
-            for (int j = 0; j < CLUSTER_SLOTS; j++) {
-                if (bitmapTestBit(hdr->myslots, j)) {
-                    if (server.cluster->slots[j] == sender || isSlotUnclaimed(j)) continue;
-                    if (server.cluster->slots[j]->configEpoch > sender_claimed_config_epoch) {
+            int found_new_owner = 0;
+            for (size_t w = 0; w < CLUSTER_SLOT_WORDS && !found_new_owner; w++) {
+                uint64_t word;
+                memcpy(&word, hdr->myslots + (w << 3), sizeof(word));
+                while (word) {
+                    /* Get the index of the least-significant set bit, in this 64-bit word */
+                    const unsigned bit = (unsigned)__builtin_ctzll(word);
+                    const int slot = (int)((w << 6) | bit);
+                    word &= word - 1; /* clear that bit */
+
+                    clusterNode *slot_owner = server.cluster->slots[slot];
+                    if (slot_owner == sender || isSlotUnclaimed(slot)) continue;
+                    if (slot_owner->configEpoch > sender_claimed_config_epoch) {
                         serverLog(LL_VERBOSE,
                                   "Node %.40s (%s) has old slots configuration, sending "
                                   "an UPDATE message about %.40s (%s)",
                                   sender->name, sender->human_nodename,
-                                  server.cluster->slots[j]->name, server.cluster->slots[j]->human_nodename);
-                        clusterSendUpdate(sender->link, server.cluster->slots[j]);
+                                  slot_owner->name, slot_owner->human_nodename);
+                        clusterSendUpdate(sender->link, slot_owner);
 
                         /* TODO: instead of exiting the loop send every other
                          * UPDATE packet for other nodes that are the new owner
                          * of sender's slots. */
+                        found_new_owner = 1;
                         break;
                     }
                 }
@@ -5003,7 +5013,8 @@ void clusterSendFailoverAuthIfNeeded(clusterNode *node, clusterMsg *request) {
     uint64_t requestConfigEpoch = ntohu64(request->configEpoch);
     unsigned char *claimed_slots = request->myslots;
     int force_ack = request->mflags[0] & CLUSTERMSG_FLAG0_FORCEACK;
-    int j;
+    int slot;
+    clusterNode *slot_owner;
 
     /* IF we are not a primary serving at least 1 slot, we don't have the
      * right to vote, as the cluster size is the number
@@ -5049,30 +5060,38 @@ void clusterSendFailoverAuthIfNeeded(clusterNode *node, clusterMsg *request) {
     /* The replica requesting the vote must have a configEpoch for the claimed
      * slots that is >= the one of the primaries currently serving the same
      * slots in the current configuration. */
-    for (j = 0; j < CLUSTER_SLOTS; j++) {
-        if (bitmapTestBit(claimed_slots, j) == 0) continue;
-        if (isSlotUnclaimed(j) || server.cluster->slots[j]->configEpoch <= requestConfigEpoch) {
-            continue;
+    for (size_t w = 0; w < CLUSTER_SLOT_WORDS; w++) {
+        uint64_t word;
+        memcpy(&word, claimed_slots + (w << 3), sizeof(word));
+        while (word) {
+            /* Get the index of the least-significant set bit, in this 64-bit word */
+            const unsigned bit = (unsigned)__builtin_ctzll(word);
+            slot = (int)((w << 6) | bit);
+            word &= word - 1; /* clear that bit */
+
+            if (isSlotUnclaimed(slot) || server.cluster->slots[slot]->configEpoch <= requestConfigEpoch) {
+                continue;
+            }
+            slot_owner = server.cluster->slots[slot];
+            /* If we reached this point we found a slot that in our current slots
+             * is served by a primary with a greater configEpoch than the one claimed
+             * by the replica requesting our vote. Refuse to vote for this replica. */
+            serverLog(LL_WARNING,
+                      "Failover auth denied to %.40s (%s): "
+                      "slot %d epoch (%llu) > reqConfigEpoch (%llu)",
+                      node->name, node->human_nodename, slot, (unsigned long long)slot_owner->configEpoch,
+                      (unsigned long long)requestConfigEpoch);
+
+            /* Send an UPDATE message to the replica. After receiving the UPDATE message,
+             * the replica will update the slots config so that it can initiate a failover
+             * again later. Otherwise the replica will never get votes if the primary is down. */
+            serverLog(LL_VERBOSE,
+                      "Node %.40s (%s) has old slots configuration, sending "
+                      "an UPDATE message about %.40s (%s)",
+                      node->name, node->human_nodename, slot_owner->name, slot_owner->human_nodename);
+            clusterSendUpdate(node->link, slot_owner);
+            return;
         }
-        /* If we reached this point we found a slot that in our current slots
-         * is served by a primary with a greater configEpoch than the one claimed
-         * by the replica requesting our vote. Refuse to vote for this replica. */
-        serverLog(LL_WARNING,
-                  "Failover auth denied to %.40s (%s): "
-                  "slot %d epoch (%llu) > reqConfigEpoch (%llu)",
-                  node->name, node->human_nodename, j, (unsigned long long)server.cluster->slots[j]->configEpoch,
-                  (unsigned long long)requestConfigEpoch);
-
-        /* Send an UPDATE message to the replica. After receiving the UPDATE message,
-         * the replica will update the slots config so that it can initiate a failover
-         * again later. Otherwise the replica will never get votes if the primary is down. */
-        serverLog(LL_VERBOSE,
-                  "Node %.40s (%s) has old slots configuration, sending "
-                  "an UPDATE message about %.40s (%s)",
-                  node->name, node->human_nodename,
-                  server.cluster->slots[j]->name, server.cluster->slots[j]->human_nodename);
-        clusterSendUpdate(node->link, server.cluster->slots[j]);
-        return;
     }
 
     /* We can vote for this replica. */