refactor: drop the unused per-lcore RCU persistent flag

e2e_test/phases/phase16_rcu_concurrency.sh

@@ -1,19 +1,12 @@
 #!/usr/bin/env bash
 # shellcheck shell=bash
 # ---------------------------------------------------------------------------
-# Phase 16 — RCU reader/writer concurrency under data-plane load
+# Phase 16 — subscriber-count churn under data-plane load
 #
-# Exercises the per-lcore persistent-online RCU getter fast path: a high-rate
-# iperf3 flow keeps the data-plane lcores hammering PPPD_GET_CCB / DHCP / stats
-# getters (RCU readers on the fast path, reporting quiescent once per burst),
-# while SetSubscriberCount is fired repeatedly — each call makes fastrg realloc
-# the ppp_ccb / dhcp_ccb / per_subscriber_stats arrays and run
-# rte_rcu_qsbr_synchronize (the RCU writer).
-#
-# If fast-path readers stopped reporting quiescent, synchronize would block and
-# SetSubscriberCount would hang; if a reader saw a freed array the node would
-# crash. Both steps passing under sustained load confirms reader/writer
-# concurrency is correct.
+# A high-rate iperf3 flow keeps the data-plane lcores busy while
+# SetSubscriberCount is fired repeatedly; each change enables or disables
+# preallocated subscriber slots on the control thread. The node must not hang
+# or crash, and the data plane must keep forwarding afterwards.
 # ---------------------------------------------------------------------------
 # Helper: restore the subscriber count churned by the Step 67 loop below +
 # stop the iperf3 server. Idempotent (set_subscriber_count/pkill both tolerate

src/dp.c

@@ -255,8 +255,6 @@ static struct rte_eth_conf port_conf_default = {
     .intr_conf = {
         .lsc = 1, /**< link status interrupt feature enabled */ },
 };
-/* Per-lcore persistent-online flag for the RCU getter fast path (see fastrg.h). */
-BOOL fastrg_rcu_persistent[RTE_MAX_LCORE];
 
 static int lsi_event_callback(U16 port_id, enum rte_eth_event_type type, void *param);
 
@@ -2227,11 +2225,10 @@ void wan_ctrl_tx(FastRG_t *fastrg_ccb, U16 ccb_id, U8 *mu, U16 mulen)
     pkt->pkt_len = mulen;
     count_tx_packet(fastrg_ccb, pkt, WAN_PORT, ccb_id);
     unsigned int lcore_id = rte_lcore_id();
-    /* Control TX callers must run on an EAL lcore. Persistent data-plane
-     * lcores are already pdump_rcu-online. Callback removal does not wait, so
-     * this window covers ctrl_thread's queue-0 TX burst in teardown's
+    /* Control TX callers must run on an EAL lcore. Callback removal does not
+     * wait, so this window covers ctrl_thread's queue-0 TX burst in teardown's
      * synchronize-before-free grace period. */
-    BOOL rcu_toggle = (lcore_id != LCORE_ID_ANY) && !fastrg_rcu_persistent[lcore_id];
+    BOOL rcu_toggle = (lcore_id != LCORE_ID_ANY);
     if (rcu_toggle)
         rte_rcu_qsbr_thread_online(fastrg_ccb->pdump_rcu, lcore_id);
     U16 cp_tx_q = fastrg_ccb->dp_ctrl_txq_cp[WAN_PORT];
@@ -2271,11 +2268,10 @@ void lan_ctrl_tx(FastRG_t *fastrg_ccb, U16 ccb_id, U8 *mu, U16 mulen)
     pkt->pkt_len = mulen;
     count_tx_packet(fastrg_ccb, pkt, LAN_PORT, ccb_id);
     unsigned int lcore_id = rte_lcore_id();
-    /* Control TX callers must run on an EAL lcore. Persistent data-plane
-     * lcores are already pdump_rcu-online. Callback removal does not wait, so
-     * this window covers ctrl_thread's queue-0 TX burst in teardown's
+    /* Control TX callers must run on an EAL lcore. Callback removal does not
+     * wait, so this window covers ctrl_thread's queue-0 TX burst in teardown's
      * synchronize-before-free grace period. */
-    BOOL rcu_toggle = (lcore_id != LCORE_ID_ANY) && !fastrg_rcu_persistent[lcore_id];
+    BOOL rcu_toggle = (lcore_id != LCORE_ID_ANY);
     if (rcu_toggle)
         rte_rcu_qsbr_thread_online(fastrg_ccb->pdump_rcu, lcore_id);
     U16 cp_tx_q = fastrg_ccb->dp_ctrl_txq_cp[LAN_PORT];

src/dp.h

@@ -532,7 +532,6 @@ static inline void fastrg_rcu_dp_online(FastRG_t *fastrg_ccb)
 static inline void fastrg_rcu_dp_register(FastRG_t *fastrg_ccb)
 {
     fastrg_rcu_dp_online(fastrg_ccb);
-    fastrg_rcu_persistent[rte_lcore_id()] = TRUE;   /* online first, then flip flag */
 }
 
 /**
@@ -557,8 +556,8 @@ static inline void fastrg_rcu_dp_quiescent(FastRG_t *fastrg_ccb)
 /**
  * @fn fastrg_rcu_dp_unregister
  *
- * @brief Report QSBR-offline on both RCUs for the calling data-plane lcore
- *        and clear its persistent flag.  MUST be called once when the thread
+ * @brief Report QSBR-offline on both RCUs for the calling data-plane lcore.
+ *        MUST be called once when the thread
  *        leaves its poll loop (on stop_flag), before returning.  Without this
  *        the thread exits while still recorded online, and the cleanup-path
  *        rte_rcu_qsbr_synchronize() waits on it forever (it never reports
@@ -570,7 +569,6 @@ static inline void fastrg_rcu_dp_quiescent(FastRG_t *fastrg_ccb)
  */
 static inline void fastrg_rcu_dp_unregister(FastRG_t *fastrg_ccb)
 {
-    fastrg_rcu_persistent[rte_lcore_id()] = FALSE;  /* flag first, then go offline */
     fastrg_rcu_dp_offline(fastrg_ccb);
 }
 

src/fastrg.h

@@ -49,13 +49,6 @@ enum {
 extern rte_atomic16_t stop_flag;
 extern rte_atomic16_t start_flag;
 
-/* Set TRUE per data-plane lcore at thread startup (fastrg_rcu_dp_register).
- * When set, the RCU ccb/stats getters take a lean load-only fast path: the lcore
- * stays QSBR-online for its whole life and reports quiescent once per burst,
- * instead of entering/exiting a critical section on every getter call.
- * Control-plane / metrics threads leave it FALSE and use the full path. */
-extern BOOL fastrg_rcu_persistent[RTE_MAX_LCORE];
-
 #define NIC_MODEL_MAX_LEN 128
 
 struct nic_info {

unit_test/dnsd/dnsd_test.c

@@ -333,7 +333,6 @@ static void dns_tcp_env_init(FastRG_t *fastrg_ccb)
     }
     memset(fastrg_ccb->per_subscriber_stats, 0,
         sizeof(fastrg_ccb->per_subscriber_stats));
-    fastrg_rcu_persistent[rte_lcore_id()] = TRUE;
 }
 
 static void dns_tcp_ctx_init(dns_tcp_ctx_t *c, FastRG_t *fastrg_ccb)
@@ -765,7 +764,6 @@ static void dns_udp_env_init(FastRG_t *fastrg_ccb)
     memset(fastrg_ccb->per_subscriber_stats, 0,
         sizeof(fastrg_ccb->per_subscriber_stats));
     fastrg_ccb->per_subscriber_stats[rte_lcore_id()][WAN_PORT] = &dns_udp_wan_stats;
-    fastrg_rcu_persistent[rte_lcore_id()] = TRUE;
 }
 
 static void dns_udp_packet_init(dns_udp_ctx_t *c, FastRG_t *fastrg_ccb)

unit_test/dp_test.c

@@ -208,7 +208,6 @@ static void test_send2cp(FastRG_t *fastrg_ccb)
     tFastRG_MBX *received = NULL;
     void *object = NULL;
     unsigned int lcore_id = rte_lcore_id();
-    BOOL old_persistent;
     struct per_ccb_stats *old_lan_stats;
     struct per_ccb_stats *old_wan_stats;
     unsigned int available_before;
@@ -218,10 +217,8 @@ static void test_send2cp(FastRG_t *fastrg_ccb)
     printf("\nTesting send2cp function:\n");
 
     TEST_ASSERT(lcore_id != LCORE_ID_ANY, "send2cp runs on an EAL lcore", "unit test should run on EAL lcore 0");
-    old_persistent = fastrg_rcu_persistent[lcore_id];
     old_lan_stats = fastrg_ccb->per_subscriber_stats[lcore_id][LAN_PORT];
     old_wan_stats = fastrg_ccb->per_subscriber_stats[lcore_id][WAN_PORT];
-    fastrg_rcu_persistent[lcore_id] = TRUE;
     fastrg_ccb->per_subscriber_stats[lcore_id][LAN_PORT] = NULL;
     fastrg_ccb->per_subscriber_stats[lcore_id][WAN_PORT] = NULL;
 
@@ -282,7 +279,6 @@ static void test_send2cp(FastRG_t *fastrg_ccb)
     fastrg_ccb->free_mail_ring = old_free_mail_ring;
     fastrg_ccb->per_subscriber_stats[lcore_id][LAN_PORT] = old_lan_stats;
     fastrg_ccb->per_subscriber_stats[lcore_id][WAN_PORT] = old_wan_stats;
-    fastrg_rcu_persistent[lcore_id] = old_persistent;
 }
 
 /* Two lcores writing one TX queue corrupt its ring, so the layout must never

unit_test/pppd/codec_test.c

@@ -1443,12 +1443,10 @@ static void decode_env_init(FastRG_t *fastrg_ccb)
     }
 
     /* The mock FastRG_t is malloc'd, so the per-lcore stats grid is garbage —
-     * wipe it and install one WAN row. The persistent-RCU flag makes the
-     * stats getter skip the (unset) stats qsbr on this lcore. */
+     * wipe it and install one WAN row. */
     memset(fastrg_ccb->per_subscriber_stats, 0,
         sizeof(fastrg_ccb->per_subscriber_stats));
     fastrg_ccb->per_subscriber_stats[rte_lcore_id()][WAN_PORT] = &decode_wan_stats;
-    fastrg_rcu_persistent[rte_lcore_id()] = TRUE;
 }
 
 static void decode_ccb_reset(FastRG_t *fastrg_ccb, U8 phase)

unit_test/pppd/pppd_test.c

@@ -50,7 +50,6 @@ static void pppd_env_init(FastRG_t *fastrg_ccb)
     }
     memset(fastrg_ccb->per_subscriber_stats, 0,
         sizeof(fastrg_ccb->per_subscriber_stats));
-    fastrg_rcu_persistent[rte_lcore_id()] = TRUE;
     rte_timer_subsystem_init();
     fastrg_ccb->lcore.ctrl_thread = rte_lcore_id();
 

unit_test/test.c

@@ -20,6 +20,7 @@ void free_ccb(FastRG_t *ccb)
     }
     if (ccb->ppp_ccb) fastrg_mfree(ccb->ppp_ccb);
     if (ccb->dhcp_ccb) fastrg_mfree(ccb->dhcp_ccb);
+    if (ccb->pdump_rcu) fastrg_mfree(ccb->pdump_rcu);
     fastrg_mfree(ccb);
 }
 
@@ -57,6 +58,18 @@ FastRG_t *init_ccb(int user_count)
     rte_rcu_qsbr_thread_register(ppp_rcu, 0);
     ccb->ppp_ccb_rcu = ppp_rcu;
 
+    /* ---- pdump_rcu ---------------------------------------------------- */
+    ccb->pdump_rcu = fastrg_calloc(struct rte_rcu_qsbr, 1, rcu_sz, RTE_CACHE_LINE_SIZE);
+    if (ccb->pdump_rcu == NULL)
+        goto err;
+    if (rte_rcu_qsbr_init(ccb->pdump_rcu, RTE_MAX_LCORE) != 0)
+        goto err;
+    unsigned int lcore_id;
+    RTE_LCORE_FOREACH(lcore_id) {
+        if (rte_rcu_qsbr_thread_register(ccb->pdump_rcu, lcore_id) != 0)
+            goto err;
+    }
+
     /* ---- ppp_ccb pointer array + individual CCBs --------------------- */
     ccb->ppp_ccb = fastrg_calloc(ppp_ccb_t *, user_count, sizeof(ppp_ccb_t *), 0);
     if (ccb->ppp_ccb == NULL) goto err;