git: 8eb4403e9d4a - main - iavf: Honor iflib transmit completion batching

The branch main has been updated by kbowling:

URL: https://cgit.FreeBSD.org/src/commit/?id=8eb4403e9d4a35f33a0ce41067ccb1924c6960dd

commit 8eb4403e9d4a35f33a0ce41067ccb1924c6960dd
Author:     Kevin Bowling <kbowling@FreeBSD.org>
AuthorDate: 2026-08-10 07:31:56 +0000
Commit:     Kevin Bowling <kbowling@FreeBSD.org>
CommitDate: 2026-08-10 08:32:56 +0000

    iavf: Honor iflib transmit completion batching
    
    iavf uses descriptor writeback by default.  Hardware writes completion
    status into a transmit descriptor only when it completes a descriptor
    marked RS.  iavf marked every packet RS even though its report-status
    queue recorded and inspected only descriptors selected by iflib.  The
    other completion writes could not help reclaim descriptors.
    
    iflib marks selected packets with IPI_TX_INTR as completion
    checkpoints.  It forces a checkpoint as deferred work or ring pressure
    grows.  Retain EOP on every packet, but set RS only at those
    checkpoints.
    
    The deprecated head-writeback option on 700-series VFs gets the same
    batching: each RS checkpoint permits hardware to publish the completed
    ring head.
    
    DPDK uses the same sparse RS design.  Let iflib choose the adaptive
    interval for FreeBSD.  This is a PCIe/memory bandwidth savings.
    
    MFC after:      2 weeks
---
 sys/dev/iavf/iavf_txrx_iflib.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/sys/dev/iavf/iavf_txrx_iflib.c b/sys/dev/iavf/iavf_txrx_iflib.c
index 4707421748bc..991238b73e7a 100644
--- a/sys/dev/iavf/iavf_txrx_iflib.c
+++ b/sys/dev/iavf/iavf_txrx_iflib.c
@@ -304,8 +304,6 @@ iavf_tso_setup(struct tx_ring *txr, if_pkt_info_t pi)
 	return ((idx + 1) & (scctx->isc_ntxd[0]-1));
 }
 
-#define IAVF_TXD_CMD (IAVF_TX_DESC_CMD_EOP | IAVF_TX_DESC_CMD_RS)
-
 /**
  * iavf_isc_txd_encap - Encapsulate a Tx packet into descriptors
  * @arg: void pointer to the VSI structure
@@ -327,7 +325,7 @@ iavf_isc_txd_encap(void *arg, if_pkt_info_t pi)
 	bus_dma_segment_t *segs = pi->ipi_segs;
 	struct iavf_tx_desc	*txd = NULL;
 	int			i, j, mask, pidx_last;
-	u32			cmd, off, tx_intr;
+	u32			cmd, off, tx_intr, txd_cmd;
 
 	if (__predict_false(pi->ipi_len < IAVF_MIN_FRAME)) {
 		que->pkt_too_small++;
@@ -338,6 +336,9 @@ iavf_isc_txd_encap(void *arg, if_pkt_info_t pi)
 	i = pi->ipi_pidx;
 
 	tx_intr = (pi->ipi_flags & IPI_TX_INTR);
+	txd_cmd = IAVF_TX_DESC_CMD_EOP;
+	if (tx_intr)
+		txd_cmd |= IAVF_TX_DESC_CMD_RS;
 
 	/* Set up the TSO/CSUM offload */
 	if (pi->ipi_csum_flags & CSUM_OFFLOAD) {
@@ -384,7 +385,7 @@ iavf_isc_txd_encap(void *arg, if_pkt_info_t pi)
 	}
 	/* Set the last descriptor for report */
 	txd->cmd_type_offset_bsz |=
-	    htole64(((u64)IAVF_TXD_CMD << IAVF_TXD_QW1_CMD_SHIFT));
+	    htole64((u64)txd_cmd << IAVF_TXD_QW1_CMD_SHIFT);
 	/* Add to report status array (if using TX interrupts) */
 	if (!vsi->enable_head_writeback && tx_intr) {
 		txr->tx_rsq[txr->tx_rs_pidx] = pidx_last;