When i use the i40e PMD to set the mtu, as follows:
1.  rte_eth_dev_ stop
2.  rte_eth_dev_set_mtu
3.  rte_eth_dev_start
The 1 and 2 steps are normal, but step 3 fails.
Log as follows:

i40e_alloc_rx queue mbufs(): Failed to allocate mbuf for RX
i40e alloc_rx queue mbufs(): Failed to allocate mbuf for RX
i40e dev rx queue start(): Failed to allocate RX queue mbuf
i40e dev switch queues(): Failed to switch rx queues
i40e dev start): Failed to enable VsI
i40e dev rx queue start(): Failed to allocate Rx queue mbuf
i40e dev switch queues(): Failed to switch rx queues
i40e dev start(): Failed to enable VSI

I don't know why?Sometimes it's normal and sometimes it's not.Only X710 nics
has the issue.