<snip>

quoted

int n = txq->tx_rs_thresh;
 int32_t i = 0, j = 0;
const int32_t k = RTE_ALIGN_FLOOR(n, RTE_I40E_TX_MAX_FREE_BUF_SZ);
const int32_t m = n % RTE_I40E_TX_MAX_FREE_BUF_SZ; struct rte_mbuf
*free[RTE_I40E_TX_MAX_FREE_BUF_SZ];

For FAST_FREE_MODE:

if (k) {
 	for (j = 0; j != k - RTE_I40E_TX_MAX_FREE_BUF_SZ;
 			j += RTE_I40E_TX_MAX_FREE_BUF_SZ) {
		for (i = 0; i <RTE_I40E_TX_MAX_FREE_BUF_SZ; ++i, ++txep) {
			free[i] = txep->mbuf;
			txep->mbuf = NULL;
		}
 		rte_mempool_put_bulk(free[0]->pool, (void **)free,
 					RTE_I40E_TX_MAX_FREE_BUF_SZ);
 	}
 }

if (m) {
 	for (i = 0; i < m; ++i, ++txep) {
		free[i] = txep->mbuf;
 		txep->mbuf = NULL;
	}
 }
 rte_mempool_put_bulk(free[0]->pool, (void **)free, m); }

Seems no logical problem, but the code looks heavy due to for loops.
Did you run performance with this change when tx_rs_thresh >
RTE_I40E_TX_MAX_FREE_BUF_SZ?

Sorry for my late rely. It takes me some time to do the test for this path and following
is my test results:

First, I come up with another way to solve this bug and compare it with "loop"(size of 'free' is 64).
That is set the size of 'free' as a large constant. We know:
tx_rs_thresh < ring_desc_size < I40E_MAX_RING_DESC(4096), so we can directly define as:
struct rte_mbuf *free[RTE_I40E_TX_MAX_FREE_BUF_SZ];

[1]Test Config:
MRR Test: two porst & bi-directional flows & one core
RX API: i40e_recv_pkts_bulk_alloc
TX API: i40e_xmit_pkts_simple
ring_descs_size: 1024
Ring_I40E_TX_MAX_FREE_SZ: 64

[2]Scheme:
tx_rs_thresh =  I40E_DEFAULT_TX_RSBIT_THRESH
tx_free_thresh = I40E_DEFAULT_TX_FREE_THRESH
tx_rs_thresh <= tx_free_thresh < nb_tx_desc
So we change the value of 'tx_rs_thresh' by adjust I40E_DEFAULT_TX_RSBIT_THRESH

[3]Test Results (performance improve):
In X86:						
tx_rs_thresh/ tx_free_thresh                       32/32          256/256          512/512
1.mempool_put(base)                                   0                  0                        0
2.mempool_put_bulk:loop                           +4.7%         +5.6%               +7.0%
3.mempool_put_bulk:large size for free   +3.8%          +2.3%               -2.0%
(free[I40E_MAX_RING_DESC])

In Arm:
N1SDP:
tx_rs_thresh/ tx_free_thresh                       32/32          256/256          512/512
1.mempool_put(base)                                   0                  0                        0
2.mempool_put_bulk:loop                           +7.9%         +9.1%               +2.9%
3.mempool_put_bulk:large size for free    +7.1%         +8.7%               +3.4%
(free[I40E_MAX_RING_DESC])

Thunderx2:
tx_rs_thresh/ tx_free_thresh                       32/32          256/256          512/512
1.mempool_put(base)                                   0                  0                        0
2.mempool_put_bulk:loop                           +7.6%         +10.5%             +7.6%
3.mempool_put_bulk:large size for free    +1.7%         +18.4%             +10.2%
(free[I40E_MAX_RING_DESC])

As a result, I feel maybe 'loop' is better and it seems not very heavy according to the test.
What about your views and look forward to your reply.
Thanks a lot.