Changes to use word-based bitwise processing for slot updates

src/cluster_legacy.c

@@ -2997,6 +2997,16 @@ static void clusterLogSlotRangeMigration(int first_slot,
               target_node->name, humanNodename(target_node), target_node->shard_id);
 }
 
+/* When iterating through the slot bitmap, group every 64 bits as
+ * a word to speedup. */
+static inline int clusterExtractSlotFromWord(uint64_t *slot_word, size_t slot_word_index) {
+    /* Get the index of the least-significant set bit, in this 64-bit word */
+    const unsigned bit = (unsigned)__builtin_ctzll(*slot_word);
+    const int slot = (int)((slot_word_index << 6) | bit);
+    *slot_word &= *slot_word - 1; /* clear that bit */
+    return slot;
+}
+
 /* This function is called when we receive a primary configuration via a
  * PING, PONG or UPDATE packet. What we receive is a node, a configEpoch of the
  * node, and the set of slots claimed under this configEpoch.
@@ -3047,8 +3057,25 @@ void clusterUpdateSlotsConfigWith(clusterNode *sender, uint64_t senderConfigEpoc
     int first_migrated_slot = -1, last_migrated_slot = -1;
     clusterNode *migration_source_node = NULL;
 
-    for (j = 0; j < CLUSTER_SLOTS; j++) {
-        if (bitmapTestBit(slots, j)) {
+    for (size_t w = 0; w < CLUSTER_SLOT_WORDS; w++) {
+        uint64_t msg_word;
+        uint64_t old_word;
+
+        /* Load 64 slots at once from the incoming message */
+        memcpy(&msg_word, slots + SLOT_WORD_OFFSET(w), sizeof(msg_word));
+        memrev64ifbe(&msg_word);
+
+        /* Load our local record of sender's slots */
+        memcpy(&old_word, sender->slots + SLOT_WORD_OFFSET(w), sizeof(old_word));
+        memrev64ifbe(&old_word);
+
+        /* Performance: If nothing changed and no slots are involved, skip 64 slots. */
+        if (msg_word == 0 && old_word == 0) continue;
+
+        /* Process only the set bits in the message word */
+        uint64_t current_msg_word = msg_word;
+        while (current_msg_word) {
+            j = clusterExtractSlotFromWord(&current_msg_word, w);
             sender_slots++;
 
             /* The slot is already bound to the sender of this message. */
@@ -3149,7 +3176,12 @@ void clusterUpdateSlotsConfigWith(clusterNode *sender, uint64_t senderConfigEpoc
                 bitmapClearBit(server.cluster->owner_not_claiming_slot, j);
                 clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG | CLUSTER_TODO_UPDATE_STATE | CLUSTER_TODO_FSYNC_CONFIG);
             }
-        } else {
+        }
+
+        /* Logic for slots in this word that are NOT in the message but were in our config */
+        uint64_t lost_slots = old_word & ~msg_word;
+        while (lost_slots) {
+            j = clusterExtractSlotFromWord(&lost_slots, w);
             if (server.cluster->slots[j] == sender) {
                 /* The slot is currently bound to the sender but the sender is no longer
                  * claiming it. We don't want to unbind the slot yet as it can cause the cluster
@@ -3792,16 +3824,6 @@ int clusterIsValidPacket(clusterLink *link) {
     return 1;
 }
 
-/* When iterating through the slot bitmap, group every 64 bits as
- * a word to speedup. */
-static inline int clusterExtractSlotFromWord(uint64_t *slot_word, size_t slot_word_index) {
-    /* Get the index of the least-significant set bit, in this 64-bit word */
-    const unsigned bit = (unsigned)__builtin_ctzll(*slot_word);
-    const int slot = (int)((slot_word_index << 6) | bit);
-    *slot_word &= *slot_word - 1; /* clear that bit */
-    return slot;
-}
-
 /* When this function is called, there is a packet to process starting
  * at link->rcvbuf. Releasing the buffer is up to the caller, so this
  * function should just handle the higher level stuff of processing the