+ flow_table = rcu_dereference(rxqueue->rps_flow_table);
+ sock_flow_table = rcu_dereference(rps_sock_flow_table);
+ if (flow_table && sock_flow_table) {
+ u16 next_cpu;
+ struct rps_dev_flow *rflow;
+
+ rflow = &flow_table->flows[skb->rxhash & flow_table->mask];
+ tcpu = rflow->cpu;
+
+ next_cpu = sock_flow_table->ents[skb->rxhash &
+ sock_flow_table->mask];
+
+ /*
+ * If the desired CPU (where last recvmsg was done) is
+ * different from current CPU (one in the rx-queue flow
+ * table entry), switch if one of the following holds:
+ * - Current CPU is unset (equal to RPS_NO_CPU).
+ * - Current CPU is offline.
+ * - The current CPU's queue tail has advanced beyond the
+ * last packet that was enqueued using this table entry.
+ * This guarantees that all previous packets for the flow
+ * have been dequeued, thus preserving in order delivery.
+ */
+ if (unlikely(tcpu != next_cpu) &&
+ (tcpu == RPS_NO_CPU || !cpu_online(tcpu) ||
+ ((int)(per_cpu(softnet_data, tcpu).input_queue_head -
+ rflow->last_qtail)) >= 0)) {
+ tcpu = rflow->cpu = next_cpu;
+ if (tcpu != RPS_NO_CPU)
+ rflow->last_qtail = per_cpu(softnet_data,
+ tcpu).input_queue_head;
+ }
+ if (tcpu != RPS_NO_CPU && cpu_online(tcpu)) {
+ *rflowp = rflow;
+ cpu = tcpu;
+ goto done;
+ }
+ }
+