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trace功能

在使能trace功能后，发现dpdk-input的feature节点是没有开启trace的，因为

查看代码\vpp-1701\vnet\vnet\devices\dpdk\node.c

关键函数是

static_always_inline u32dpdk_device_input (dpdk_main_t * dm, dpdk_device_t * xd,		   vlib_node_runtime_t * node, u32 cpu_index, u16 queue_id){  ......  while (n_buffers > 0)    {      ......      vlib_get_next_frame (vm, node, next_index, to_next, n_left_to_next);      while (n_buffers > 8 && n_left_to_next > 4)	{		}          while (n_buffers > 0 && n_left_to_next > 0)	{	  /* Do we have any driver RX features configured on the interface? */	  vnet_feature_start_device_input_x1 (xd->vlib_sw_if_index, &next0,					      b0, l3_offset0);	  vlib_validate_buffer_enqueue_x1 (vm, node, next_index,					   to_next, n_left_to_next,					   bi0, next0);	  n_buffers--;	  mb_index++;	}      vlib_put_next_frame (vm, node, next_index, n_left_to_next);    }  if (PREDICT_FALSE (vec_len (xd->d_trace_buffers[cpu_index]) > 0))    {      dpdk_rx_trace (dm, node, xd, queue_id, xd->d_trace_buffers[cpu_index],		     vec_len (xd->d_trace_buffers[cpu_index]));      vlib_set_trace_count (vm, node, n_trace -			    vec_len (xd->d_trace_buffers[cpu_index]));    }  vlib_increment_combined_counter    (vnet_get_main ()->interface_main.combined_sw_if_counters     + VNET_INTERFACE_COUNTER_RX,     cpu_index, xd->vlib_sw_if_index, mb_index, n_rx_bytes);  dpdk_worker_t *dw = vec_elt_at_index (dm->workers, cpu_index);  dw->aggregate_rx_packets += mb_index;  return mb_index;}

dpdk_rx_trace开始使能node trace，注意上面函数dpdk_rx_trace函数的执行位置。

if (PREDICT_FALSE (vec_len (xd->d_trace_buffers[cpu_index]) > 0))    {      dpdk_rx_trace (dm, node, xd, queue_id, xd->d_trace_buffers[cpu_index],		     vec_len (xd->d_trace_buffers[cpu_index]));      vlib_set_trace_count (vm, node, n_trace -			    vec_len (xd->d_trace_buffers[cpu_index]));    }

在dpdk-input node 后添加feature node 后，vlib_put_next_frame (vm, node, next_index, n_left_to_next)中 next_index,会是feature node的索引，

而dpdk_rx_trace里的下一节点索引还是默认的，所以feature node 就不会trace了

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