vio: Increase rx mbuf size with lro

bluhm found that using bigger rx mbufs helps tcp splice performance if
lro is enabled. Use 4k in that case.

Also fix confusion in rx dmamap segment count. Even with lro/tso, we
only put unfragmented mbufs into the rx queue. Therefore we only need
max. 2 segments, one for the mbuf and one for the separate header for
legacy virtio devices.

OK bluhm@

diff --git a/sys/dev/pv/if_vio.c b/sys/dev/pv/if_vio.c
index 9b6a545..06ad4b8 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 1.56 2024/09/19 06:23:38 sf Exp $  */
+/*     $OpenBSD: if_vio.c,v 1.57 2024/10/03 08:59:49 sf Exp $  */
 
 /*
  * Copyright (c) 2012 Stefan Fritsch, Alexander Fiveg.
@@ -256,6 +256,7 @@ struct vio_softc {
 
        struct vio_queue        *sc_q;
        uint16_t                sc_nqueues;
+       int                     sc_rx_mbuf_size;
 
        enum vio_ctrl_state     sc_ctrl_inuse;
 
@@ -492,8 +493,9 @@ vio_alloc_mem(struct vio_softc *sc, int tx_max_segments)
                vioq->viq_txmbufs = vioq->viq_rxmbufs + rxqsize;
 
                for (i = 0; i < rxqsize; i++) {
-                       r = bus_dmamap_create(vsc->sc_dmat, MAXMCLBYTES,
-                           MAXMCLBYTES/PAGE_SIZE + 1, MCLBYTES, 0,
+                       r = bus_dmamap_create(vsc->sc_dmat,
+                           sc->sc_rx_mbuf_size + sc->sc_hdr_size, 2,
+                           sc->sc_rx_mbuf_size, 0,
                            BUS_DMA_NOWAIT|BUS_DMA_ALLOCNOW,
                            &vioq->viq_rxdmamaps[i]);
                        if (r != 0)
@@ -644,10 +646,35 @@ vio_attach(struct device *parent, struct device *self, void *aux)
        } else {
                sc->sc_hdr_size = offsetof(struct virtio_net_hdr, num_buffers);
        }
+
+       ifp->if_capabilities = 0;
+       ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
+#if NVLAN > 0
+       ifp->if_capabilities |= IFCAP_VLAN_MTU;
+       ifp->if_capabilities |= IFCAP_VLAN_HWOFFLOAD;
+#endif
+       if (virtio_has_feature(vsc, VIRTIO_NET_F_CSUM))
+               ifp->if_capabilities |= IFCAP_CSUM_TCPv4|IFCAP_CSUM_UDPv4|
+                   IFCAP_CSUM_TCPv6|IFCAP_CSUM_UDPv6;
+       if (virtio_has_feature(vsc, VIRTIO_NET_F_HOST_TSO4))
+               ifp->if_capabilities |= IFCAP_TSOv4;
+       if (virtio_has_feature(vsc, VIRTIO_NET_F_HOST_TSO6))
+               ifp->if_capabilities |= IFCAP_TSOv6;
+
+       sc->sc_rx_mbuf_size = MCLBYTES;
+       if (virtio_has_feature(vsc, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) &&
+           (virtio_has_feature(vsc, VIRTIO_NET_F_GUEST_TSO4) ||
+            virtio_has_feature(vsc, VIRTIO_NET_F_GUEST_TSO6))) {
+               ifp->if_xflags |= IFXF_LRO;
+               ifp->if_capabilities |= IFCAP_LRO;
+               sc->sc_rx_mbuf_size = 4 * 1024;
+       }
+
        if (virtio_has_feature(vsc, VIRTIO_NET_F_MRG_RXBUF))
                ifp->if_hardmtu = MAXMCLBYTES;
        else
-               ifp->if_hardmtu = MCLBYTES - sc->sc_hdr_size - ETHER_HDR_LEN;
+               ifp->if_hardmtu = sc->sc_rx_mbuf_size - sc->sc_hdr_size -
+                   ETHER_HDR_LEN;
 
        /* defrag for longer mbuf chains */
        tx_max_segments = 16;
@@ -699,28 +726,8 @@ vio_attach(struct device *parent, struct device *self, void *aux)
 
        strlcpy(ifp->if_xname, self->dv_xname, IFNAMSIZ);
        ifp->if_softc = sc;
-       ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
        ifp->if_start = vio_start;
        ifp->if_ioctl = vio_ioctl;
-       ifp->if_capabilities = 0;
-#if NVLAN > 0
-       ifp->if_capabilities |= IFCAP_VLAN_MTU;
-       ifp->if_capabilities |= IFCAP_VLAN_HWOFFLOAD;
-#endif
-       if (virtio_has_feature(vsc, VIRTIO_NET_F_CSUM))
-               ifp->if_capabilities |= IFCAP_CSUM_TCPv4|IFCAP_CSUM_UDPv4|
-                   IFCAP_CSUM_TCPv6|IFCAP_CSUM_UDPv6;
-       if (virtio_has_feature(vsc, VIRTIO_NET_F_HOST_TSO4))
-               ifp->if_capabilities |= IFCAP_TSOv4;
-       if (virtio_has_feature(vsc, VIRTIO_NET_F_HOST_TSO6))
-               ifp->if_capabilities |= IFCAP_TSOv6;
-
-       if (virtio_has_feature(vsc, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) &&
-           (virtio_has_feature(vsc, VIRTIO_NET_F_GUEST_TSO4) ||
-            virtio_has_feature(vsc, VIRTIO_NET_F_GUEST_TSO6))) {
-               ifp->if_xflags |= IFXF_LRO;
-               ifp->if_capabilities |= IFCAP_LRO;
-       }
 
        ifq_init_maxlen(&ifp->if_snd, vsc->sc_vqs[1].vq_num - 1);
        ifmedia_init(&sc->sc_media, 0, vio_media_change, vio_media_status);
@@ -808,7 +815,7 @@ vio_init(struct ifnet *ifp)
                struct vio_queue *vioq = &sc->sc_q[qidx];
 
                if_rxr_init(&vioq->viq_rxring,
-                   2 * ((ifp->if_hardmtu / MCLBYTES) + 1),
+                   2 * ((ifp->if_hardmtu / sc->sc_rx_mbuf_size) + 1),
                    vioq->viq_rxvq->vq_num);
                vio_populate_rx_mbufs(sc, vioq);
        }
@@ -1102,7 +1109,7 @@ vio_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
                break;
        case SIOCGIFRXR:
                r = if_rxr_ioctl((struct if_rxrinfo *)ifr->ifr_data,
-                   NULL, MCLBYTES, &sc->sc_q[0].viq_rxring);
+                   NULL, sc->sc_rx_mbuf_size, &sc->sc_q[0].viq_rxring);
                break;
        default:
                r = ether_ioctl(ifp, &sc->sc_ac, cmd, data);
@@ -1127,7 +1134,7 @@ vio_add_rx_mbuf(struct vio_softc *sc, struct vio_queue *vioq, int i)
        struct mbuf *m;
        int r;
 
-       m = MCLGETL(NULL, M_DONTWAIT, MCLBYTES);
+       m = MCLGETL(NULL, M_DONTWAIT, sc->sc_rx_mbuf_size);
        if (m == NULL)
                return ENOBUFS;
        vioq->viq_rxmbufs[i] = m;
@@ -1199,7 +1206,8 @@ vio_populate_rx_mbufs(struct vio_softc *sc, struct vio_queue *vioq)
                        virtio_enqueue_p(vq, slot, vioq->viq_rxdmamaps[slot],
                            0, sc->sc_hdr_size, 0);
                        virtio_enqueue_p(vq, slot, vioq->viq_rxdmamaps[slot],
-                           sc->sc_hdr_size, MCLBYTES - sc->sc_hdr_size, 0);
+                           sc->sc_hdr_size,
+                           sc->sc_rx_mbuf_size - sc->sc_hdr_size, 0);
                }
                virtio_enqueue_commit(vsc, vq, slot, 0);
                done = 1;