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diff --git a/share/man/man4/iflib.4 b/share/man/man4/iflib.4
--- a/share/man/man4/iflib.4
+++ b/share/man/man4/iflib.4
@@ -1,4 +1,4 @@
-.Dd September 27, 2018
+.Dd August 20, 2025
.Dt IFLIB 4
.Os
.Sh NAME
@@ -64,6 +64,18 @@
core.
When set to a non-zero value, TX queues are assigned to cores following the
last RX queue.
+.It Va simple_tx
+When set to one, iflib uses a simple transmit routine with no queuing at all.
+By default, iflib uses a highly optimized, lockless, transmit queue called
+mp_ring.
+This performs well when there are more CPU cores than NIC
+queues and prevents lock contention for transmit resources.
+Unfortunately, mp_ring incurs unneeded overheads on workloads where
+resource contention is not a problem (well behaved applications on
+systems where there are as many NIC queues as CPU cores).
+Note that when this is enabled, the tx_abdicate sysctl is no longer
+applicable and is ignored.
+Defaults to zero.
.El
.Pp
These
diff --git a/sys/net/iflib.c b/sys/net/iflib.c
--- a/sys/net/iflib.c
+++ b/sys/net/iflib.c
@@ -142,6 +142,7 @@
static void iru_init(if_rxd_update_t iru, iflib_rxq_t rxq, uint8_t flid);
static void iflib_timer(void *arg);
static void iflib_tqg_detach(if_ctx_t ctx);
+static int iflib_simple_transmit(if_t ifp, struct mbuf *m);
typedef struct iflib_filter_info {
driver_filter_t *ifi_filter;
@@ -198,6 +199,7 @@
uint8_t ifc_sysctl_use_logical_cores;
uint16_t ifc_sysctl_extra_msix_vectors;
bool ifc_cpus_are_physical_cores;
+ bool ifc_sysctl_simple_tx;
qidx_t ifc_sysctl_ntxds[8];
qidx_t ifc_sysctl_nrxds[8];
@@ -725,6 +727,7 @@
#ifndef __NO_STRICT_ALIGNMENT
static struct mbuf *iflib_fixup_rx(struct mbuf *m);
#endif
+static __inline int iflib_completed_tx_reclaim(iflib_txq_t txq, int thresh);
static SLIST_HEAD(cpu_offset_list, cpu_offset) cpu_offsets =
SLIST_HEAD_INITIALIZER(cpu_offsets);
@@ -2624,8 +2627,10 @@
#endif /* DEV_NETMAP */
CALLOUT_UNLOCK(txq);
- /* clean any enqueued buffers */
- iflib_ifmp_purge(txq);
+ if (!ctx->ifc_sysctl_simple_tx) {
+ /* clean any enqueued buffers */
+ iflib_ifmp_purge(txq);
+ }
/* Free any existing tx buffers. */
for (j = 0; j < txq->ift_size; j++) {
iflib_txsd_free(ctx, txq, j);
@@ -3635,13 +3640,16 @@
* cxgb
*/
if (__predict_false(nsegs + 2 > TXQ_AVAIL(txq))) {
- txq->ift_no_desc_avail++;
- bus_dmamap_unload(buf_tag, map);
- DBG_COUNTER_INC(encap_txq_avail_fail);
- DBG_COUNTER_INC(encap_txd_encap_fail);
- if ((txq->ift_task.gt_task.ta_flags & TASK_ENQUEUED) == 0)
- GROUPTASK_ENQUEUE(&txq->ift_task);
- return (ENOBUFS);
+ (void)iflib_completed_tx_reclaim(txq, RECLAIM_THRESH(ctx));
+ if (__predict_false(nsegs + 2 > TXQ_AVAIL(txq))) {
+ txq->ift_no_desc_avail++;
+ bus_dmamap_unload(buf_tag, map);
+ DBG_COUNTER_INC(encap_txq_avail_fail);
+ DBG_COUNTER_INC(encap_txd_encap_fail);
+ if ((txq->ift_task.gt_task.ta_flags & TASK_ENQUEUED) == 0)
+ GROUPTASK_ENQUEUE(&txq->ift_task);
+ return (ENOBUFS);
+ }
}
/*
* On Intel cards we can greatly reduce the number of TX interrupts
@@ -4014,6 +4022,12 @@
netmap_tx_irq(ifp, txq->ift_id))
goto skip_ifmp;
#endif
+ if (ctx->ifc_sysctl_simple_tx) {
+ mtx_lock(&txq->ift_mtx);
+ (void)iflib_completed_tx_reclaim(txq, RECLAIM_THRESH(ctx));
+ mtx_unlock(&txq->ift_mtx);
+ goto skip_ifmp;
+ }
#ifdef ALTQ
if (if_altq_is_enabled(ifp))
iflib_altq_if_start(ifp);
@@ -4027,9 +4041,8 @@
*/
if (abdicate)
ifmp_ring_check_drainage(txq->ift_br, TX_BATCH_SIZE);
-#ifdef DEV_NETMAP
+
skip_ifmp:
-#endif
if (ctx->ifc_flags & IFC_LEGACY)
IFDI_INTR_ENABLE(ctx);
else
@@ -5131,7 +5144,14 @@
scctx = &ctx->ifc_softc_ctx;
ifp = ctx->ifc_ifp;
-
+ if (ctx->ifc_sysctl_simple_tx) {
+#ifndef ALTQ
+ if_settransmitfn(ifp, iflib_simple_transmit);
+ device_printf(dev, "using simple if_transmit\n");
+#else
+ device_printf(dev, "ALTQ prevents using simple if_transmit\n");
+#endif
+ }
iflib_reset_qvalues(ctx);
IFNET_WLOCK();
CTX_LOCK(ctx);
@@ -6766,6 +6786,9 @@
SYSCTL_ADD_CONST_STRING(ctx_list, oid_list, OID_AUTO, "driver_version",
CTLFLAG_RD, ctx->ifc_sctx->isc_driver_version, "driver version");
+ SYSCTL_ADD_BOOL(ctx_list, oid_list, OID_AUTO, "simple_tx",
+ CTLFLAG_RDTUN, &ctx->ifc_sysctl_simple_tx, 0,
+ "use simple tx ring");
SYSCTL_ADD_U16(ctx_list, oid_list, OID_AUTO, "override_ntxqs",
CTLFLAG_RWTUN, &ctx->ifc_sysctl_ntxqs, 0,
"# of txqs to use, 0 => use default #");
@@ -7088,3 +7111,48 @@
return (0);
}
#endif /* DEBUGNET */
+
+
+static inline iflib_txq_t
+iflib_simple_select_queue(if_ctx_t ctx, struct mbuf *m)
+{
+ int qidx;
+
+ if ((NTXQSETS(ctx) > 1) && M_HASHTYPE_GET(m))
+ qidx = QIDX(ctx, m);
+ else
+ qidx = NTXQSETS(ctx) + FIRST_QSET(ctx) - 1;
+ return (&ctx->ifc_txqs[qidx]);
+}
+
+static int
+iflib_simple_transmit(if_t ifp, struct mbuf *m)
+{
+ if_ctx_t ctx;
+ iflib_txq_t txq;
+ int error;
+ int bytes_sent = 0, pkt_sent = 0, mcast_sent = 0;
+
+
+ ctx = if_getsoftc(ifp);
+ if ((if_getdrvflags(ifp) & (IFF_DRV_RUNNING | IFF_DRV_OACTIVE)) !=
+ IFF_DRV_RUNNING)
+ return (EBUSY);
+ txq = iflib_simple_select_queue(ctx, m);
+ mtx_lock(&txq->ift_mtx);
+ error = iflib_encap(txq, &m);
+ if (error == 0) {
+ pkt_sent++;
+ bytes_sent += m->m_pkthdr.len;
+ mcast_sent += !!(m->m_flags & M_MCAST);
+ (void)iflib_txd_db_check(txq, true);
+ }
+ (void)iflib_completed_tx_reclaim(txq, RECLAIM_THRESH(ctx));
+ mtx_unlock(&txq->ift_mtx);
+ if_inc_counter(ifp, IFCOUNTER_OBYTES, bytes_sent);
+ if_inc_counter(ifp, IFCOUNTER_OPACKETS, pkt_sent);
+ if (mcast_sent)
+ if_inc_counter(ifp, IFCOUNTER_OMCASTS, mcast_sent);
+
+ return (error);
+}

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