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Index: share/man/man4/iflib.4
===================================================================
--- share/man/man4/iflib.4
+++ share/man/man4/iflib.4
@@ -1,4 +1,4 @@
-.Dd August 8, 2026
+.Dd August 26, 2026
.Dt IFLIB 4
.Os
.Sh NAME
@@ -131,10 +131,13 @@
.It Va net.iflib.tx_watchdog_periods
Number of consecutive
.Va net.iflib.timer_default
-intervals for which a transmit queue must stay frozen,
-that is, hold descriptors the hardware has not reported as completed
-while none are reclaimed,
-before iflib asks the hardware whether it has completions pending.
+intervals for which a transmit queue must remain frozen under demand before
+iflib asks the hardware whether it has completions pending.
+A queue is frozen when it holds descriptors the hardware has not reported as
+completed while none are reclaimed.
+Demand persists while the outstanding descriptor count grows, the software
+queue is stalled, or the hardware descriptor ring is at its backpressure
+threshold.
If it reports none, the interface is reset.
Setting this to zero disables the check.
.El
Index: sys/net/iflib.c
===================================================================
--- sys/net/iflib.c
+++ sys/net/iflib.c
@@ -509,6 +509,9 @@
#define TXQ_AVAIL(txq) ((txq->ift_size - txq->ift_pad) -\
get_inuse(txq->ift_size, txq->ift_cidx, txq->ift_pidx, txq->ift_gen))
+#define MAX_TX_DESC(ctx) MAX((ctx)->ifc_softc_ctx.isc_tx_tso_segments_max, \
+ (ctx)->ifc_softc_ctx.isc_tx_nsegments)
+
#define IDXDIFF(head, tail, wrap) \
((head) >= (tail) ? (head) - (tail) : (wrap) - (tail) + (head))
@@ -624,19 +627,19 @@
SYSCTL_INT(_net_iflib, OID_AUTO, timer_default, CTLFLAG_RW,
&iflib_timer_default, 0, "number of ticks between iflib_timer calls");
/*
- * Consecutive timer periods a TX queue must stay frozen - see
- * iflib_timer(), which defines that state - before the hardware is
- * asked whether it has completions pending. Four periods is roughly
- * two seconds with the default timer interval: a healthy queue on
- * hardware that coalesces completion reports (e.g. 8254x,
- * TXDCTL.WTHRESH) stays frozen for at most two (measured on 82541PI),
- * a wedged one until it is reset.
+ * Consecutive timer periods a TX queue must stay frozen while demand
+ * persists - see iflib_timer(), which defines those states - before the
+ * hardware is asked whether it has completions pending. Four periods is
+ * roughly two seconds with the default timer interval: a healthy queue on
+ * hardware that coalesces completion reports (e.g. 8254x, TXDCTL.WTHRESH)
+ * stays frozen for at most two (measured on 82541PI), a wedged one until it
+ * is reset.
*/
static int iflib_tx_watchdog_periods = 4;
SYSCTL_INT(_net_iflib, OID_AUTO, tx_watchdog_periods, CTLFLAG_RWTUN,
&iflib_tx_watchdog_periods, 0,
- "consecutive frozen timer periods before a TX queue is checked for "
- "a hang (0 disables the check)");
+ "consecutive frozen timer periods under demand before a TX queue is "
+ "checked for a hang (0 disables the check)");
#if IFLIB_DEBUG_COUNTERS
@@ -2475,8 +2478,8 @@
* delays the verdict by one timer period.
*/
if (this_tick - txq->ift_last_timer_tick >= iflib_timer_default) {
- qidx_t outstanding;
- bool frozen;
+ qidx_t in_use, outstanding;
+ bool demand, frozen;
txq->ift_last_timer_tick = this_tick;
IFDI_TIMER(ctx, txq->ift_id);
@@ -2490,7 +2493,8 @@
* reported and must not count (ift_rs_pending
* over-counts it by one per packet).
*/
- outstanding = txq->ift_in_use -
+ in_use = txq->ift_in_use;
+ outstanding = in_use -
(qidx_t)(txq->ift_processed - txq->ift_cleaned);
/*
@@ -2500,12 +2504,17 @@
* up, with no pause frames and no pending doorbell
* (the laggard check below rings it).
*
- * Being frozen is not a fault - the hardware may
- * defer marking descriptors as completed
- * indefinitely, and 8254x hardware does so for a
- * quiet queue - therefore the check arms only when a
- * frozen queue also takes on new work, and acts only
- * once it has stayed frozen for
+ * Being frozen is not a fault - the hardware may defer
+ * marking descriptors as completed indefinitely, and
+ * 8254x hardware does so for a quiet queue. Continue
+ * arming only while demand persists: the outstanding
+ * count grows, the software ring is stalled, or the
+ * hardware ring has reached iflib's backpressure
+ * threshold. The last condition covers simple-TX, which
+ * does not use the software ring. This also prevents one
+ * mixed lockless counter sample from arming a quiet queue
+ * until the verdict. Act only once it has stayed frozen
+ * under demand for
* net.iflib.tx_watchdog_periods consecutive periods.
*/
frozen = outstanding > txq->ift_rs_pending &&
@@ -2513,10 +2522,12 @@
txq->ift_db_pending == 0 &&
sctx->isc_pause_frames == 0 &&
ctx->ifc_link_state == LINK_STATE_UP;
- if (!frozen)
+ demand = outstanding > txq->ift_outstanding_prev ||
+ ifmp_ring_is_stalled(txq->ift_br) ||
+ in_use + MAX_TX_DESC(ctx) >= txq->ift_size - txq->ift_pad;
+ if (!frozen || !demand)
txq->ift_wdog_armed = 0;
- else if (txq->ift_wdog_armed > 0 ||
- outstanding > txq->ift_outstanding_prev) {
+ else {
if (txq->ift_wdog_armed < UINT16_MAX)
txq->ift_wdog_armed++;
}
@@ -2525,8 +2536,8 @@
* Frozen long enough: ask the hardware. Completions
* ready but unharvested for this long mean the
* completion interrupt went missing - kick the
- * queue's task. Nothing ready, although the queue
- * kept taking on work, means it is hung.
+ * queue's task. Nothing ready while demand persisted
+ * means it is hung.
*/
if (iflib_tx_watchdog_periods > 0 &&
txq->ift_wdog_armed >= iflib_tx_watchdog_periods) {
@@ -3246,9 +3257,6 @@
#define QIDX(ctx, m) ((((m)->m_pkthdr.flowid & ctx->ifc_softc_ctx.isc_rss_table_mask) % NTXQSETS(ctx)) + FIRST_QSET(ctx))
#define DESC_RECLAIMABLE(q) ((int)((q)->ift_processed - (q)->ift_cleaned - (q)->ift_ctx->ifc_softc_ctx.isc_tx_nsegments))
-#define MAX_TX_DESC(ctx) MAX((ctx)->ifc_softc_ctx.isc_tx_tso_segments_max, \
- (ctx)->ifc_softc_ctx.isc_tx_nsegments)
-
static inline bool
iflib_txd_db_check(iflib_txq_t txq, int ring)
{

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