tighten up the tx start/completion handling of the producer and consumer.

the hypervisor obvious snoops the descriptor rings like crazy, and
it can run and complete transmit of packets as soon as the ownership
bit is set on the descriptor and before the txh register is updated
with the producer index. txintr would only process tx completions
if the producer and consumer indexes the driver maintains were
different, but would then go and pop every packet the hardware said
was done off the ring.

this changes txintr so it will only iterate over packets between
the driver consumer and producer indexes. also, have the start code
update the producer before flipping the ownership bit in the ring.
this keeps the start and intr code in sync.

diff --git a/sys/dev/pci/if_vmx.c b/sys/dev/pci/if_vmx.c
index 5053e6b..ffceccf 100644 (file)
--- a/sys/dev/pci/if_vmx.c
+++ b/sys/dev/pci/if_vmx.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: if_vmx.c,v 1.71 2023/07/30 01:15:42 dlg Exp $ */
+/*     $OpenBSD: if_vmx.c,v 1.72 2023/07/30 01:41:05 dlg Exp $ */
 
 /*
  * Copyright (c) 2013 Tsubai Masanari
@@ -68,8 +68,8 @@ struct vmxnet3_txring {
        bus_dmamap_t dmap[NTXDESC];
        struct vmxnet3_txdesc *txd;
        u_int32_t gen;
-       u_int prod;
-       u_int cons;
+       volatile u_int prod;
+       volatile u_int cons;
 };
 
 struct vmxnet3_rxring {
@@ -927,18 +927,20 @@ vmxnet3_txintr(struct vmxnet3_softc *sc, struct vmxnet3_txqueue *tq)
        struct vmxnet3_txcompdesc *txcd;
        bus_dmamap_t map;
        struct mbuf *m;
-       u_int cons, next;
+       u_int prod, cons, next;
        uint32_t rgen;
 
+       prod = ring->prod;
        cons = ring->cons;
-       if (cons == ring->prod)
+
+       if (cons == prod)
                return;
 
        next = comp_ring->next;
        rgen = comp_ring->gen;
 
        /* postread */
-       for (;;) {
+       do {
                txcd = &comp_ring->txcd[next];
                if ((txcd->txc_word3 & VMX_TXC_GEN) != rgen)
                        break;
@@ -961,7 +963,7 @@ vmxnet3_txintr(struct vmxnet3_softc *sc, struct vmxnet3_txqueue *tq)
                    VMXNET3_TXC_EOPIDX_M;
                cons++;
                cons %= NTXDESC;
-       }
+       } while (cons != prod);
        /* preread */
 
        comp_ring->next = next;
@@ -1394,6 +1396,7 @@ vmxnet3_start(struct ifqueue *ifq)
                            VMXNET3_TX_VLANTAG_M) << VMXNET3_TX_VLANTAG_S);
                }
 
+               ring->prod = prod;
                /* Change the ownership by flipping the "generation" bit */
                membar_producer();
                sop->tx_word2 ^= VMX_TX_GEN;
@@ -1405,7 +1408,6 @@ vmxnet3_start(struct ifqueue *ifq)
        if (!post)
                return;
 
-       ring->prod = prod;
        ring->gen = rgen;
 
        WRITE_BAR0(sc, VMXNET3_BAR0_TXH(tq->queue), prod);