snat: thread safe (VPP-443)

All traffic corresponding to a specific SANT user is handled by a CPU core.
in2out: Non-translated packets worker lookup by src address and VRF hash in
snat-in2out-worker-handoff node.
out2in: Translated packets worker lookup by dst address and port number hash in
snat-out2in-worker-handoff node.

Change-Id: Ia092a605689539469841d382588f3f486a29a769
Signed-off-by: Matus Fabian <matfabia@cisco.com>

1 files changed, 278 insertions, 72 deletions

diff --git a/plugins/snat-plugin/snat/in2out.c b/plugins/snat-plugin/snat/in2out.c
index 9a4aeb01fd4..e1edbb81581 100644
--- a/plugins/snat-plugin/snat/in2out.c
+++ b/plugins/snat-plugin/snat/in2out.c
@@ -16,6 +16,7 @@
 #include <vlib/vlib.h>
 #include <vnet/vnet.h>
 #include <vnet/pg/pg.h>
+#include <vnet/handoff.h>
 
 #include <vnet/ip/ip.h>
 #include <vnet/ethernet/ethernet.h>
@@ -33,6 +34,11 @@ typedef struct {
   u32 is_slow_path;
 } snat_in2out_trace_t;
 
+typedef struct {
+  u32 next_worker_index;
+  u8 do_handoff;
+} snat_in2out_worker_handoff_trace_t;
+
 /* packet trace format function */
 static u8 * format_snat_in2out_trace (u8 * s, va_list * args)
 {
@@ -61,9 +67,24 @@ static u8 * format_snat_in2out_fast_trace (u8 * s, va_list * args)
   return s;
 }
 
+static u8 * format_snat_in2out_worker_handoff_trace (u8 * s, va_list * args)
+{
+  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
+  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
+  snat_in2out_worker_handoff_trace_t * t =
+    va_arg (*args, snat_in2out_worker_handoff_trace_t *);
+  char * m;
+
+  m = t->do_handoff ? "next worker" : "same worker";
+  s = format (s, "SNAT_IN2OUT_WORKER_HANDOFF: %s %d", m, t->next_worker_index);
+
+  return s;
+}
+
 vlib_node_registration_t snat_in2out_node;
 vlib_node_registration_t snat_in2out_slowpath_node;
 vlib_node_registration_t snat_in2out_fast_node;
+vlib_node_registration_t snat_in2out_worker_handoff_node;
 
 #define foreach_snat_in2out_error                       \
 _(UNSUPPORTED_PROTOCOL, "Unsupported protocol")         \
@@ -93,14 +114,14 @@ typedef enum {
   SNAT_IN2OUT_N_NEXT,
 } snat_in2out_next_t;
 
-
 static u32 slow_path (snat_main_t *sm, vlib_buffer_t *b0,
                       ip4_header_t * ip0,
                       u32 rx_fib_index0,
                       snat_session_key_t * key0,
                       snat_session_t ** sessionp,
                       vlib_node_runtime_t * node,
-                      u32 next0)
+                      u32 next0,
+                      u32 cpu_index)
 {
   snat_user_t *u;
   snat_user_key_t user_key;
@@ -115,6 +136,7 @@ static u32 slow_path (snat_main_t *sm, vlib_buffer_t *b0,
   u32 address_index = ~0;
   u32 outside_fib_index;
   uword * p;
+  snat_static_mapping_key_t worker_by_out_key;
 
   p = hash_get (sm->ip4_main->fib_index_by_table_id, sm->outside_vrf_id);
   if (! p)
@@ -132,25 +154,27 @@ static u32 slow_path (snat_main_t *sm, vlib_buffer_t *b0,
   if (clib_bihash_search_8_8 (&sm->user_hash, &kv0, &value0))
     {
       /* no, make a new one */
-      pool_get (sm->users, u);
+      pool_get (sm->per_thread_data[cpu_index].users, u);
       memset (u, 0, sizeof (*u));
       u->addr = ip0->src_address;
 
-      pool_get (sm->list_pool, per_user_list_head_elt);
+      pool_get (sm->per_thread_data[cpu_index].list_pool, per_user_list_head_elt);
 
       u->sessions_per_user_list_head_index = per_user_list_head_elt -
-        sm->list_pool;
+        sm->per_thread_data[cpu_index].list_pool;
 
-      clib_dlist_init (sm->list_pool, u->sessions_per_user_list_head_index);
+      clib_dlist_init (sm->per_thread_data[cpu_index].list_pool,
+                       u->sessions_per_user_list_head_index);
 
-      kv0.value = u - sm->users;
+      kv0.value = u - sm->per_thread_data[cpu_index].users;
 
       /* add user */
       clib_bihash_add_del_8_8 (&sm->user_hash, &kv0, 1 /* is_add */);
     }
   else
     {
-      u = pool_elt_at_index (sm->users, value0.value);
+      u = pool_elt_at_index (sm->per_thread_data[cpu_index].users,
+                             value0.value);
     }
 
   /* Over quota? Recycle the least recently used dynamic translation */
@@ -159,25 +183,26 @@ static u32 slow_path (snat_main_t *sm, vlib_buffer_t *b0,
       /* Remove the oldest dynamic translation */
       do {
           oldest_per_user_translation_list_index =
-            clib_dlist_remove_head
-            (sm->list_pool, u->sessions_per_user_list_head_index);
+            clib_dlist_remove_head (sm->per_thread_data[cpu_index].list_pool,
+                                    u->sessions_per_user_list_head_index);
 
           ASSERT (oldest_per_user_translation_list_index != ~0);
 
           /* add it back to the end of the LRU list */
-          clib_dlist_addtail (sm->list_pool,
+          clib_dlist_addtail (sm->per_thread_data[cpu_index].list_pool,
                               u->sessions_per_user_list_head_index,
                               oldest_per_user_translation_list_index);
           /* Get the list element */
           oldest_per_user_translation_list_elt =
-            pool_elt_at_index (sm->list_pool,
+            pool_elt_at_index (sm->per_thread_data[cpu_index].list_pool,
                                oldest_per_user_translation_list_index);
 
           /* Get the session index from the list element */
           session_index = oldest_per_user_translation_list_elt->value;
 
           /* Get the session */
-          s = pool_elt_at_index (sm->sessions, session_index);
+          s = pool_elt_at_index (sm->per_thread_data[cpu_index].sessions,
+                                 session_index);
       } while (!snat_is_session_static (s));
 
       /* Remove in2out, out2in keys */
@@ -218,7 +243,7 @@ static u32 slow_path (snat_main_t *sm, vlib_buffer_t *b0,
         }
 
       /* Create a new session */
-      pool_get (sm->sessions, s);
+      pool_get (sm->per_thread_data[cpu_index].sessions, s);
       memset (s, 0, sizeof (*s));
       
       s->outside_address_index = address_index;
@@ -234,16 +259,22 @@ static u32 slow_path (snat_main_t *sm, vlib_buffer_t *b0,
         }
 
       /* Create list elts */
-      pool_get (sm->list_pool, per_user_translation_list_elt);
-      clib_dlist_init (sm->list_pool, per_user_translation_list_elt -
-                       sm->list_pool);
-
-      per_user_translation_list_elt->value = s - sm->sessions;
-      s->per_user_index = per_user_translation_list_elt - sm->list_pool;
+      pool_get (sm->per_thread_data[cpu_index].list_pool,
+                per_user_translation_list_elt);
+      clib_dlist_init (sm->per_thread_data[cpu_index].list_pool,
+                       per_user_translation_list_elt -
+                       sm->per_thread_data[cpu_index].list_pool);
+
+      per_user_translation_list_elt->value =
+        s - sm->per_thread_data[cpu_index].sessions;
+      s->per_user_index = per_user_translation_list_elt -
+                          sm->per_thread_data[cpu_index].list_pool;
       s->per_user_list_head_index = u->sessions_per_user_list_head_index;
 
-      clib_dlist_addtail (sm->list_pool, s->per_user_list_head_index,
-                          per_user_translation_list_elt - sm->list_pool);
+      clib_dlist_addtail (sm->per_thread_data[cpu_index].list_pool,
+                          s->per_user_list_head_index,
+                          per_user_translation_list_elt -
+                          sm->per_thread_data[cpu_index].list_pool);
    }
   
   s->in2out = *key0;
@@ -254,16 +285,23 @@ static u32 slow_path (snat_main_t *sm, vlib_buffer_t *b0,
 
   /* Add to translation hashes */
   kv0.key = s->in2out.as_u64;
-  kv0.value = s - sm->sessions;
+  kv0.value = s - sm->per_thread_data[cpu_index].sessions;
   if (clib_bihash_add_del_8_8 (&sm->in2out, &kv0, 1 /* is_add */))
       clib_warning ("in2out key add failed");
   
   kv0.key = s->out2in.as_u64;
-  kv0.value = s - sm->sessions;
+  kv0.value = s - sm->per_thread_data[cpu_index].sessions;
   
   if (clib_bihash_add_del_8_8 (&sm->out2in, &kv0, 1 /* is_add */))
       clib_warning ("out2in key add failed");
 
+  /* Add to translated packets worker lookup */
+  worker_by_out_key.addr = s->out2in.addr;
+  worker_by_out_key.port = s->out2in.port;
+  worker_by_out_key.fib_index = s->out2in.fib_index;
+  kv0.key = worker_by_out_key.as_u64;
+  kv0.value = cpu_index;
+  clib_bihash_add_del_8_8 (&sm->worker_by_out, &kv0, 1);
   return next0;
 }
                       
@@ -275,7 +313,8 @@ static inline u32 icmp_in2out_slow_path (snat_main_t *sm,
                                          u32 rx_fib_index0,
                                          vlib_node_runtime_t * node,
                                          u32 next0,
-                                         f64 now)
+                                         f64 now,
+                                         u32 cpu_index)
 {
   snat_session_key_t key0;
   icmp_echo_header_t *echo0;
@@ -320,13 +359,14 @@ static inline u32 icmp_in2out_slow_path (snat_main_t *sm,
         return next0;
       
       next0 = slow_path (sm, b0, ip0, rx_fib_index0, &key0,
-                         &s0, node, next0);
+                         &s0, node, next0, cpu_index);
       
       if (PREDICT_FALSE (next0 == SNAT_IN2OUT_NEXT_DROP))
         return next0;
     }
   else
-    s0 = pool_elt_at_index (sm->sessions, value0.value);
+    s0 = pool_elt_at_index (sm->per_thread_data[cpu_index].sessions,
+                            value0.value);
 
   old_addr0 = ip0->src_address.as_u32;
   ip0->src_address = s0->out2in.addr;
@@ -355,8 +395,10 @@ static inline u32 icmp_in2out_slow_path (snat_main_t *sm,
   /* Per-user LRU list maintenance for dynamic translations */
   if (!snat_is_session_static (s0))
     {
-      clib_dlist_remove (sm->list_pool, s0->per_user_index);
-      clib_dlist_addtail (sm->list_pool, s0->per_user_list_head_index,
+      clib_dlist_remove (sm->per_thread_data[cpu_index].list_pool,
+                         s0->per_user_index);
+      clib_dlist_addtail (sm->per_thread_data[cpu_index].list_pool,
+                          s0->per_user_list_head_index,
                           s0->per_user_index);
     }
 
@@ -375,6 +417,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
   snat_runtime_t * rt = (snat_runtime_t *)node->runtime_data;
   f64 now = vlib_time_now (vm);
   u32 stats_node_index;
+  u32 cpu_index = os_get_cpu_number ();
 
   stats_node_index = is_slow_path ? snat_in2out_slowpath_node.index :
     snat_in2out_node.index;
@@ -445,14 +488,6 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 
           next0 = next1 = SNAT_IN2OUT_NEXT_LOOKUP;
 
-#if 0
-          /* Formally correct, but we send to slowpath, lookup or drop */
-	  vnet_get_config_data (&cm->config_main,
-                                &b0->current_config_index,
-                                &next0,
-                                0 /* sizeof config data */);
-#endif
-
           proto0 = ~0;
           proto0 = (ip0->protocol == IP_PROTOCOL_UDP) 
             ? SNAT_PROTOCOL_UDP : proto0;
@@ -471,7 +506,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
                 {
                   next0 = icmp_in2out_slow_path 
                     (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, 
-                     node, next0, now);
+                     node, next0, now, cpu_index);
                   goto trace00;
                 }
             }
@@ -512,7 +547,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
                     goto trace00;
                   
                   next0 = slow_path (sm, b0, ip0, rx_fib_index0, &key0,
-                                     &s0, node, next0);
+                                     &s0, node, next0, cpu_index);
                   if (PREDICT_FALSE (next0 == SNAT_IN2OUT_NEXT_DROP))
                     goto trace00;
                 }
@@ -523,7 +558,8 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
                 }
             }
           else
-            s0 = pool_elt_at_index (sm->sessions, value0.value);
+            s0 = pool_elt_at_index (sm->per_thread_data[cpu_index].sessions,
+                                    value0.value);
 
           old_addr0 = ip0->src_address.as_u32;
           ip0->src_address = s0->out2in.addr;
@@ -565,8 +601,10 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
           /* Per-user LRU list maintenance for dynamic translation */
           if (!snat_is_session_static (s0))
             {
-              clib_dlist_remove (sm->list_pool, s0->per_user_index);
-              clib_dlist_addtail (sm->list_pool, s0->per_user_list_head_index,
+              clib_dlist_remove (sm->per_thread_data[cpu_index].list_pool,
+                                 s0->per_user_index);
+              clib_dlist_addtail (sm->per_thread_data[cpu_index].list_pool,
+                                  s0->per_user_list_head_index,
                                   s0->per_user_index);
             }
         trace00:
@@ -581,7 +619,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               t->next_index = next0;
                   t->session_index = ~0;
               if (s0)
-                  t->session_index = s0 - sm->sessions;
+                t->session_index = s0 - sm->per_thread_data[cpu_index].sessions;
             }
 
           pkts_processed += next0 != SNAT_IN2OUT_NEXT_DROP;
@@ -595,13 +633,6 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 	  rx_fib_index1 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index, 
                                    sw_if_index1);
 
-#if 0
-	  vnet_get_config_data (&cm->config_main,
-                                &b1->current_config_index,
-                                &next1,
-                                0 /* sizeof config data */);
-#endif
-
           proto1 = ~0;
           proto1 = (ip1->protocol == IP_PROTOCOL_UDP) 
             ? SNAT_PROTOCOL_UDP : proto1;
@@ -619,8 +650,8 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               if (PREDICT_FALSE (proto1 == SNAT_PROTOCOL_ICMP))
                 {
                   next1 = icmp_in2out_slow_path 
-                    (sm, b1, ip1, icmp1, sw_if_index1, rx_fib_index1, node, next1,
-                     now);
+                    (sm, b1, ip1, icmp1, sw_if_index1, rx_fib_index1, node,
+                     next1, now, cpu_index);
                   goto trace01;
                 }
             }
@@ -661,7 +692,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
                     goto trace01;
                   
                   next1 = slow_path (sm, b1, ip1, rx_fib_index1, &key1,
-                                     &s1, node, next1);
+                                     &s1, node, next1, cpu_index);
                   if (PREDICT_FALSE (next1 == SNAT_IN2OUT_NEXT_DROP))
                     goto trace01;
                 }
@@ -672,7 +703,8 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
                 }
             }
           else
-            s1 = pool_elt_at_index (sm->sessions, value1.value);
+            s1 = pool_elt_at_index (sm->per_thread_data[cpu_index].sessions,
+                                    value1.value);
 
           old_addr1 = ip1->src_address.as_u32;
           ip1->src_address = s1->out2in.addr;
@@ -714,8 +746,10 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
           /* Per-user LRU list maintenance for dynamic translation */
           if (!snat_is_session_static (s1))
             {
-              clib_dlist_remove (sm->list_pool, s1->per_user_index);
-              clib_dlist_addtail (sm->list_pool, s1->per_user_list_head_index,
+              clib_dlist_remove (sm->per_thread_data[cpu_index].list_pool,
+                                 s1->per_user_index);
+              clib_dlist_addtail (sm->per_thread_data[cpu_index].list_pool,
+                                  s1->per_user_list_head_index,
                                   s1->per_user_index);
             }
         trace01:
@@ -729,7 +763,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               t->next_index = next1;
               t->session_index = ~0;
               if (s1)
-                t->session_index = s1 - sm->sessions;
+                t->session_index = s1 - sm->per_thread_data[cpu_index].sessions;
             }
 
           pkts_processed += next1 != SNAT_IN2OUT_NEXT_DROP;
@@ -779,14 +813,6 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
 	  rx_fib_index0 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index, 
                                    sw_if_index0);
 
-
-#if 0
-	  vnet_get_config_data (&cm->config_main,
-                                &b0->current_config_index,
-                                &next0,
-                                0 /* sizeof config data */);
-#endif
-
           proto0 = ~0;
           proto0 = (ip0->protocol == IP_PROTOCOL_UDP) 
             ? SNAT_PROTOCOL_UDP : proto0;
@@ -804,8 +830,8 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               if (PREDICT_FALSE (proto0 == SNAT_PROTOCOL_ICMP))
                 {
                   next0 = icmp_in2out_slow_path 
-                    (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node, next0,
-                     now);
+                    (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
+                     next0, now, cpu_index);
                   goto trace0;
                 }
             }
@@ -846,7 +872,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
                     goto trace0;
                   
                   next0 = slow_path (sm, b0, ip0, rx_fib_index0, &key0,
-                                     &s0, node, next0);
+                                     &s0, node, next0, cpu_index);
                   if (PREDICT_FALSE (next0 == SNAT_IN2OUT_NEXT_DROP))
                     goto trace0;
                 }
@@ -857,7 +883,8 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
                 }
             }
           else
-            s0 = pool_elt_at_index (sm->sessions, value0.value);
+            s0 = pool_elt_at_index (sm->per_thread_data[cpu_index].sessions,
+                                    value0.value);
 
           old_addr0 = ip0->src_address.as_u32;
           ip0->src_address = s0->out2in.addr;
@@ -899,8 +926,10 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
           /* Per-user LRU list maintenance for dynamic translation */
           if (!snat_is_session_static (s0))
             {
-              clib_dlist_remove (sm->list_pool, s0->per_user_index);
-              clib_dlist_addtail (sm->list_pool, s0->per_user_list_head_index,
+              clib_dlist_remove (sm->per_thread_data[cpu_index].list_pool,
+                                 s0->per_user_index);
+              clib_dlist_addtail (sm->per_thread_data[cpu_index].list_pool,
+                                  s0->per_user_list_head_index,
                                   s0->per_user_index);
             }
 
@@ -915,7 +944,7 @@ snat_in2out_node_fn_inline (vlib_main_t * vm,
               t->next_index = next0;
                   t->session_index = ~0;
               if (s0)
-                  t->session_index = s0 - sm->sessions;
+                t->session_index = s0 - sm->per_thread_data[cpu_index].sessions;
             }
 
           pkts_processed += next0 != SNAT_IN2OUT_NEXT_DROP;
@@ -999,6 +1028,183 @@ VLIB_REGISTER_NODE (snat_in2out_slowpath_node) = {
 
 VLIB_NODE_FUNCTION_MULTIARCH (snat_in2out_slowpath_node, snat_in2out_slow_path_fn);
 
+static uword
+snat_in2out_worker_handoff_fn (vlib_main_t * vm,
+                               vlib_node_runtime_t * node,
+                               vlib_frame_t * frame)
+{
+  snat_main_t *sm = &snat_main;
+  vlib_thread_main_t *tm = vlib_get_thread_main ();
+  u32 n_left_from, *from, *to_next = 0;
+  static __thread vlib_frame_queue_elt_t **handoff_queue_elt_by_worker_index;
+  static __thread vlib_frame_queue_t **congested_handoff_queue_by_worker_index
+    = 0;
+  vlib_frame_queue_elt_t *hf = 0;
+  vlib_frame_t *f = 0;
+  int i;
+  u32 n_left_to_next_worker = 0, *to_next_worker = 0;
+  u32 next_worker_index = 0;
+  u32 current_worker_index = ~0;
+  u32 cpu_index = os_get_cpu_number ();
+
+  if (PREDICT_FALSE (handoff_queue_elt_by_worker_index == 0))
+    {
+      vec_validate (handoff_queue_elt_by_worker_index, tm->n_vlib_mains - 1);
+
+      vec_validate_init_empty (congested_handoff_queue_by_worker_index,
+			       sm->first_worker_index + sm->num_workers - 1,
+			       (vlib_frame_queue_t *) (~0));
+    }
+
+  from = vlib_frame_vector_args (frame);
+  n_left_from = frame->n_vectors;
+
+  while (n_left_from > 0)
+    {
+      u32 bi0;
+      vlib_buffer_t *b0;
+      u32 sw_if_index0;
+      u32 rx_fib_index0;
+      ip4_header_t * ip0;
+      snat_user_key_t key0;
+      clib_bihash_kv_8_8_t kv0, value0;
+      u8 do_handoff;
+
+      bi0 = from[0];
+      from += 1;
+      n_left_from -= 1;
+
+      b0 = vlib_get_buffer (vm, bi0);
+
+      sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
+      rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index(sw_if_index0);
+
+      ip0 = vlib_buffer_get_current (b0);
+
+      key0.addr = ip0->src_address;
+      key0.fib_index = rx_fib_index0;
+
+      kv0.key = key0.as_u64;
+
+      /* Ever heard of of the "user" before? */
+      if (clib_bihash_search_8_8 (&sm->worker_by_in, &kv0, &value0))
+        {
+          /* No, assign next available worker (RR) */
+          next_worker_index = sm->first_worker_index +
+            sm->workers[sm->next_worker++ % vec_len (sm->workers)];
+
+          /* add non-traslated packets worker lookup */
+          kv0.value = next_worker_index;
+          clib_bihash_add_del_8_8 (&sm->worker_by_in, &kv0, 1);
+        }
+      else
+        next_worker_index = value0.value;
+
+      if (PREDICT_FALSE (next_worker_index != cpu_index))
+        {
+          do_handoff = 1;
+
+          if (next_worker_index != current_worker_index)
+            {
+              if (hf)
+                hf->n_vectors = VLIB_FRAME_SIZE - n_left_to_next_worker;
+
+              hf = vlib_get_worker_handoff_queue_elt (sm->fq_in2out_index,
+                                                      next_worker_index,
+                                                      handoff_queue_elt_by_worker_index);
+
+              n_left_to_next_worker = VLIB_FRAME_SIZE - hf->n_vectors;
+              to_next_worker = &hf->buffer_index[hf->n_vectors];
+              current_worker_index = next_worker_index;
+            }
+
+          /* enqueue to correct worker thread */
+          to_next_worker[0] = bi0;
+          to_next_worker++;
+          n_left_to_next_worker--;
+
+          if (n_left_to_next_worker == 0)
+            {
+              hf->n_vectors = VLIB_FRAME_SIZE;
+              vlib_put_frame_queue_elt (hf);
+              current_worker_index = ~0;
+              handoff_queue_elt_by_worker_index[next_worker_index] = 0;
+              hf = 0;
+            }
+        }
+      else
+        {
+          do_handoff = 0;
+          /* if this is 1st frame */
+          if (!f)
+            {
+              f = vlib_get_frame_to_node (vm, snat_in2out_node.index);
+              to_next = vlib_frame_vector_args (f);
+            }
+
+          to_next[0] = bi0;
+          to_next += 1;
+          f->n_vectors++;
+        }
+
+      if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
+			 && (b0->flags & VLIB_BUFFER_IS_TRACED)))
+	{
+          snat_in2out_worker_handoff_trace_t *t =
+            vlib_add_trace (vm, node, b0, sizeof (*t));
+          t->next_worker_index = next_worker_index;
+          t->do_handoff = do_handoff;
+        }
+    }
+
+  if (f)
+    vlib_put_frame_to_node (vm, snat_in2out_node.index, f);
+
+  if (hf)
+    hf->n_vectors = VLIB_FRAME_SIZE - n_left_to_next_worker;
+
+  /* Ship frames to the worker nodes */
+  for (i = 0; i < vec_len (handoff_queue_elt_by_worker_index); i++)
+    {
+      if (handoff_queue_elt_by_worker_index[i])
+	{
+	  hf = handoff_queue_elt_by_worker_index[i];
+	  /*
+	   * It works better to let the handoff node
+	   * rate-adapt, always ship the handoff queue element.
+	   */
+	  if (1 || hf->n_vectors == hf->last_n_vectors)
+	    {
+	      vlib_put_frame_queue_elt (hf);
+	      handoff_queue_elt_by_worker_index[i] = 0;
+	    }
+	  else
+	    hf->last_n_vectors = hf->n_vectors;
+	}
+      congested_handoff_queue_by_worker_index[i] =
+	(vlib_frame_queue_t *) (~0);
+    }
+  hf = 0;
+  current_worker_index = ~0;
+  return frame->n_vectors;
+}
+
+VLIB_REGISTER_NODE (snat_in2out_worker_handoff_node) = {
+  .function = snat_in2out_worker_handoff_fn,
+  .name = "snat-in2out-worker-handoff",
+  .vector_size = sizeof (u32),
+  .format_trace = format_snat_in2out_worker_handoff_trace,
+  .type = VLIB_NODE_TYPE_INTERNAL,
+  
+  .n_next_nodes = 1,
+
+  .next_nodes = {
+    [0] = "error-drop",
+  },
+};
+
+VLIB_NODE_FUNCTION_MULTIARCH (snat_in2out_worker_handoff_node, snat_in2out_worker_handoff_fn);
+
 static inline u32 icmp_in2out_static_map (snat_main_t *sm,
                                           vlib_buffer_t * b0,
                                           ip4_header_t * ip0,