# HG changeset patch
# User Navdeep Parhar <navdeep@chelsio.com>
# Date 1605296322 28800
#      Fri Nov 13 11:38:42 2020 -0800
# Branch freebsd-head
# Node ID e53533ab0124414f69ff4d9b3fb8fe8590d2f57f
# Parent  88d9936695dc5231e1dbc64c0445b29f87c69c1a
cxgbe(4): Knob to disable tx coalescing.

hw.cxgbe.tx_coalesce=0

diff -r 88d9936695dc -r e53533ab0124 sys/dev/cxgbe/t4_sge.c
--- a/sys/dev/cxgbe/t4_sge.c	Fri Nov 27 23:11:40 2020 -0800
+++ b/sys/dev/cxgbe/t4_sge.c	Fri Nov 13 11:38:42 2020 -0800
@@ -229,6 +229,10 @@ static counter_u64_t defrags;
 SYSCTL_COUNTER_U64(_hw_cxgbe, OID_AUTO, defrags, CTLFLAG_RD, &defrags,
     "Number of mbuf defrags performed");
 
+static int t4_tx_coalesce = 1;
+SYSCTL_INT(_hw_cxgbe, OID_AUTO, tx_coalesce, CTLFLAG_RWTUN, &t4_tx_coalesce, 0,
+    "tx coalescing allowed");
+
 
 static int service_iq(struct sge_iq *, int);
 static int service_iq_fl(struct sge_iq *, int);
@@ -3213,6 +3217,8 @@ eth_tx(struct mp_ring *r, u_int cidx, u_
 		if (avail < 2 * SGE_MAX_WR_NDESC)
 			avail += reclaim_tx_descs(txq, 64);
 
+		if (t4_tx_coalesce == 0 && txp->npkt == 0)
+			goto skip_coalescing;
 		if (txp->npkt > 0 || remaining > 1 || txp->score > 3 ||
 		    atomic_load_int(&txq->eq.equiq) != 0) {
 			if (vi->flags & TX_USES_VM_WR)
@@ -3269,7 +3275,7 @@ eth_tx(struct mp_ring *r, u_int cidx, u_
 
 		MPASS(rc != 0 && rc != EAGAIN);
 		MPASS(txp->npkt == 0);
-
+skip_coalescing:
 		n = tx_len16_to_desc(mbuf_len16(m0));
 		if (__predict_false(avail < n)) {
 			avail += reclaim_tx_descs(txq, min(n, 32));