vio: allow longer tx chains

When TCP segmentation offload is supported, we may get larger packets
with more dma segments. Allocate more segments in the busdma_map in this
case, so that we need to defragment less often.

ok jan@

diff --git a/sys/dev/pv/if_vio.c b/sys/dev/pv/if_vio.c
index e9c5f82..9b6a545 100644 (file)
--- a/sys/dev/pv/if_vio.c
+++ b/sys/dev/pv/if_vio.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: if_vio.c,v 1.55 2024/09/17 09:00:14 sf Exp $  */
+/*     $OpenBSD: if_vio.c,v 1.56 2024/09/19 06:23:38 sf Exp $  */
 
 /*
  * Copyright (c) 2012 Stefan Fritsch, Alexander Fiveg.
@@ -269,7 +269,6 @@ struct vio_softc {
 #define VIO_HAVE_MRG_RXBUF(sc)                                 \
        ((sc)->sc_hdr_size == sizeof(struct virtio_net_hdr))
 
-#define VIRTIO_NET_TX_MAXNSEGS         16 /* for larger chains, defrag */
 #define VIRTIO_NET_CTRL_MAC_MC_ENTRIES 64 /* for more entries, use ALLMULTI */
 #define VIRTIO_NET_CTRL_MAC_UC_ENTRIES  1 /* one entry for own unicast addr */
 #define VIRTIO_NET_CTRL_TIMEOUT                (5*1000*1000*1000ULL) /* 5 seconds */
@@ -321,7 +320,7 @@ int vio_ctrl_start(struct vio_softc *, uint8_t, uint8_t, int, int *);
 int    vio_ctrl_submit(struct vio_softc *, int);
 void   vio_ctrl_finish(struct vio_softc *);
 void   vio_ctrl_wakeup(struct vio_softc *, enum vio_ctrl_state);
-int    vio_alloc_mem(struct vio_softc *);
+int    vio_alloc_mem(struct vio_softc *, int);
 int    vio_alloc_dmamem(struct vio_softc *);
 void   vio_free_dmamem(struct vio_softc *);
 
@@ -416,7 +415,7 @@ vio_free_dmamem(struct vio_softc *sc)
  *   viq_txmbufs[slot]:                mbuf pointer array for sent frames
  */
 int
-vio_alloc_mem(struct vio_softc *sc)
+vio_alloc_mem(struct vio_softc *sc, int tx_max_segments)
 {
        struct virtio_softc     *vsc = sc->sc_virtio;
        struct ifnet            *ifp = &sc->sc_ac.ac_if;
@@ -503,7 +502,7 @@ vio_alloc_mem(struct vio_softc *sc)
 
                for (i = 0; i < txqsize; i++) {
                        r = bus_dmamap_create(vsc->sc_dmat, txsize,
-                           VIRTIO_NET_TX_MAXNSEGS, txsize, 0,
+                           tx_max_segments, txsize, 0,
                            BUS_DMA_NOWAIT|BUS_DMA_ALLOCNOW,
                            &vioq->viq_txdmamaps[i]);
                        if (r != 0)
@@ -586,7 +585,7 @@ vio_attach(struct device *parent, struct device *self, void *aux)
 {
        struct vio_softc *sc = (struct vio_softc *)self;
        struct virtio_softc *vsc = (struct virtio_softc *)parent;
-       int i;
+       int i, tx_max_segments;
        struct ifnet *ifp = &sc->sc_ac.ac_if;
 
        if (vsc->sc_child != NULL) {
@@ -650,6 +649,17 @@ vio_attach(struct device *parent, struct device *self, void *aux)
        else
                ifp->if_hardmtu = MCLBYTES - sc->sc_hdr_size - ETHER_HDR_LEN;
 
+       /* defrag for longer mbuf chains */
+       tx_max_segments = 16;
+       if (virtio_has_feature(vsc, VIRTIO_NET_F_HOST_TSO4) ||
+           virtio_has_feature(vsc, VIRTIO_NET_F_HOST_TSO6)) {
+               /*
+                * With TSO, we may get 64K packets and want to be able to
+                * send longer chains without defragmenting
+                */
+               tx_max_segments = 32;
+       }
+
        for (i = 0; i < sc->sc_nqueues; i++) {
                int vqidx = 2 * i;
                struct vio_queue *vioq = &sc->sc_q[i];
@@ -664,7 +674,7 @@ vio_attach(struct device *parent, struct device *self, void *aux)
                vqidx++;
                vioq->viq_txvq = &vsc->sc_vqs[vqidx];
                if (virtio_alloc_vq(vsc, vioq->viq_txvq, vqidx,
-                   VIRTIO_NET_TX_MAXNSEGS + 1, "tx") != 0) {
+                   tx_max_segments + 1, "tx") != 0) {
                        goto err;
                }
                vioq->viq_txvq->vq_done = vio_tx_intr;
@@ -684,7 +694,7 @@ vio_attach(struct device *parent, struct device *self, void *aux)
                virtio_start_vq_intr(vsc, sc->sc_ctl_vq);
        }
 
-       if (vio_alloc_mem(sc) < 0)
+       if (vio_alloc_mem(sc, tx_max_segments) < 0)
                goto err;
 
        strlcpy(ifp->if_xname, self->dv_xname, IFNAMSIZ);