[PATCH v5 31/35] net/intel: align scalar simple Tx path with vector logic

Bruce Richardson
2026-02-11T18:16:39Z

The scalar simple Tx path has the same restrictions as the vector Tx
path, so we can use the same logic flow in both, to try and ensure we
get best performance from the scalar path.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>
---
drivers/net/intel/common/tx_scalar.h | 54 +++++++++++++++++-----------
1 file changed, 34 insertions(+), 20 deletions(-)

diff --git a/drivers/net/intel/common/tx_scalar.h b/drivers/net/intel/common/tx_scalar.h
index 2c624e97e7..8f87acde25 100644
--- a/drivers/net/intel/common/tx_scalar.h
+++ b/drivers/net/intel/common/tx_scalar.h
@@ -25,13 +25,11 @@ write_txd(volatile void *txd, uint64_t qw0, uint64_t qw1)
txdesc->qw1 = rte_cpu_to_le_64(qw1);
}

-/* Fill hardware descriptor ring with mbuf data */
+/* Fill hardware descriptor ring with mbuf data (simple path) */
static inline void
-ci_tx_fill_hw_ring(struct ci_tx_queue *txq, struct rte_mbuf **pkts,
- uint16_t nb_pkts)
+ci_tx_fill_hw_ring_simple(volatile struct ci_tx_desc *txdp, struct rte_mbuf **pkts,
+ uint16_t nb_pkts)
{
- volatile struct ci_tx_desc *txdp = &txq->ci_tx_ring[txq->tx_tail];
- struct ci_tx_entry *txep = &txq->sw_ring[txq->tx_tail];
const int N_PER_LOOP = 4;
const int N_PER_LOOP_MASK = N_PER_LOOP - 1;
int mainpart, leftover;
@@ -40,8 +38,6 @@ ci_tx_fill_hw_ring(struct ci_tx_queue *txq, struct rte_mbuf **pkts,
mainpart = nb_pkts & ((uint32_t)~N_PER_LOOP_MASK);
leftover = nb_pkts & ((uint32_t)N_PER_LOOP_MASK);
for (i = 0; i < mainpart; i += N_PER_LOOP) {
- for (j = 0; j < N_PER_LOOP; ++j)
- (txep + i + j)->mbuf = *(pkts + i + j);
for (j = 0; j < N_PER_LOOP; ++j)
write_txd(txdp + i + j, rte_mbuf_data_iova(*(pkts + i + j)),
CI_TX_DESC_DTYPE_DATA |
@@ -52,12 +48,10 @@ ci_tx_fill_hw_ring(struct ci_tx_queue *txq, struct rte_mbuf **pkts,
if (unlikely(leftover > 0)) {
for (i = 0; i < leftover; ++i) {
uint16_t idx = mainpart + i;
- (txep + idx)->mbuf = *(pkts + idx);
write_txd(txdp + idx, rte_mbuf_data_iova(*(pkts + idx)),
CI_TX_DESC_DTYPE_DATA |
((uint64_t)CI_TX_DESC_CMD_DEFAULT << CI_TXD_QW1_CMD_S) |
((uint64_t)(*(pkts + idx))->data_len << CI_TXD_QW1_TX_BUF_SZ_S));
-
}
}
}
@@ -134,6 +128,9 @@ ci_xmit_burst_simple(struct ci_tx_queue *txq,
uint16_t nb_pkts)
{
volatile struct ci_tx_desc *txr = txq->ci_tx_ring;
+ volatile struct ci_tx_desc *txdp;
+ struct ci_tx_entry *txep;
+ uint16_t tx_id;
uint16_t n = 0;

/**
@@ -149,23 +146,41 @@ ci_xmit_burst_simple(struct ci_tx_queue *txq,
if (unlikely(!nb_pkts))
return 0;

+ tx_id = txq->tx_tail;
+ txdp = &txr[tx_id];
+ txep = &txq->sw_ring[tx_id];
+
txq->nb_tx_free = (uint16_t)(txq->nb_tx_free - nb_pkts);
- if ((txq->tx_tail + nb_pkts) > txq->nb_tx_desc) {
- n = (uint16_t)(txq->nb_tx_desc - txq->tx_tail);
- ci_tx_fill_hw_ring(txq, tx_pkts, n);
+
+ if ((tx_id + nb_pkts) > txq->nb_tx_desc) {
+ n = (uint16_t)(txq->nb_tx_desc - tx_id);
+
+ /* Store mbufs in backlog */
+ ci_tx_backlog_entry(txep, tx_pkts, n);
+
+ /* Write descriptors to HW ring */
+ ci_tx_fill_hw_ring_simple(txdp, tx_pkts, n);
+
txr[txq->tx_next_rs].cmd_type_offset_bsz |=
rte_cpu_to_le_64(((uint64_t)CI_TX_DESC_CMD_RS) <<
CI_TXD_QW1_CMD_S);
txq->tx_next_rs = (uint16_t)(txq->tx_rs_thresh - 1);
- txq->tx_tail = 0;
+
+ tx_id = 0;
+ txdp = &txr[tx_id];
+ txep = &txq->sw_ring[tx_id];
}

- /* Fill hardware descriptor ring with mbuf data */
- ci_tx_fill_hw_ring(txq, tx_pkts + n, (uint16_t)(nb_pkts - n));
- txq->tx_tail = (uint16_t)(txq->tx_tail + (nb_pkts - n));
+ /* Store remaining mbufs in backlog */
+ ci_tx_backlog_entry(txep, tx_pkts + n, (uint16_t)(nb_pkts - n));
+
+ /* Write remaining descriptors to HW ring */
+ ci_tx_fill_hw_ring_simple(txdp, tx_pkts + n, (uint16_t)(nb_pkts - n));
+
+ tx_id = (uint16_t)(tx_id + (nb_pkts - n));

/* Determine if RS bit needs to be set */
- if (txq->tx_tail > txq->tx_next_rs) {
+ if (tx_id > txq->tx_next_rs) {
txr[txq->tx_next_rs].cmd_type_offset_bsz |=
rte_cpu_to_le_64(((uint64_t)CI_TX_DESC_CMD_RS) <<
CI_TXD_QW1_CMD_S);
@@ -175,11 +190,10 @@ ci_xmit_burst_simple(struct ci_tx_queue *txq,
txq->tx_next_rs = (uint16_t)(txq->tx_rs_thresh - 1);
}

- if (txq->tx_tail >= txq->nb_tx_desc)
- txq->tx_tail = 0;
+ txq->tx_tail = tx_id;

/* Update the tx tail register */
- rte_write32_wc((uint32_t)txq->tx_tail, txq->qtx_tail);
+ rte_write32_wc((uint32_t)tx_id, txq->qtx_tail);

return nb_pkts;
}
--
2.51.0