While it has served us well, it is long overdue that we eliminate the virtio-net tap hack. It turns out that zero-copy has very little impact on performance. The tap hack was gaining such a significant performance boost not because of zero-copy, but because it avoided dropping packets on receive which is apparently a significant problem with the tap implementation in QEMU.
Patches 3 and 4 in this series address the packet dropping issue and the net result is a 25% boost in RX performance even in the absence of zero-copy. Also worth mentioning, is that this makes merging virtio into upstream QEMU significantly easier. Signed-off-by: Anthony Liguori <[EMAIL PROTECTED]> diff --git a/qemu/hw/pc.h b/qemu/hw/pc.h index 57d2123..f5157bd 100644 --- a/qemu/hw/pc.h +++ b/qemu/hw/pc.h @@ -154,7 +154,6 @@ void isa_ne2000_init(int base, qemu_irq irq, NICInfo *nd); /* virtio-net.c */ PCIDevice *virtio_net_init(PCIBus *bus, NICInfo *nd, int devfn); -void virtio_net_poll(void); /* virtio-blk.h */ void *virtio_blk_init(PCIBus *bus, uint16_t vendor, uint16_t device, diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c index f727b14..8d26832 100644 --- a/qemu/hw/virtio-net.c +++ b/qemu/hw/virtio-net.c @@ -13,7 +13,6 @@ #include "virtio.h" #include "net.h" -#include "pc.h" #include "qemu-timer.h" /* from Linux's virtio_net.h */ @@ -62,15 +61,10 @@ typedef struct VirtIONet VirtQueue *tx_vq; VLANClientState *vc; int can_receive; - int tap_fd; - struct VirtIONet *next; - int do_notify; QEMUTimer *tx_timer; int tx_timer_active; } VirtIONet; -static VirtIONet *VirtIONetHead = NULL; - static VirtIONet *to_virtio_net(VirtIODevice *vdev) { return (VirtIONet *)vdev; @@ -105,7 +99,6 @@ static int virtio_net_can_receive(void *opaque) return (n->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK) && n->can_receive; } -/* -net user receive function */ static void virtio_net_receive(void *opaque, const uint8_t *buf, int size) { VirtIONet *n = opaque; @@ -144,87 +137,6 @@ static void virtio_net_receive(void *opaque, const uint8_t *buf, int size) virtio_notify(&n->vdev, n->rx_vq); } -/* -net tap receive handler */ -void virtio_net_poll(void) -{ - VirtIONet *vnet; - int len; - fd_set rfds; - struct timeval tv; - int max_fd = -1; - VirtQueueElement elem; - struct virtio_net_hdr *hdr; - int did_notify; - - FD_ZERO(&rfds); - tv.tv_sec = 0; - tv.tv_usec = 0; - - while (1) { - - // Prepare the set of device to select from - for (vnet = VirtIONetHead; vnet; vnet = vnet->next) { - - if (vnet->tap_fd == -1) - continue; - - vnet->do_notify = 0; - //first check if the driver is ok - if (!virtio_net_can_receive(vnet)) - continue; - - /* FIXME: the drivers really need to set their status better */ - if (vnet->rx_vq->vring.avail == NULL) { - vnet->can_receive = 0; - continue; - } - - FD_SET(vnet->tap_fd, &rfds); - if (max_fd < vnet->tap_fd) max_fd = vnet->tap_fd; - } - - if (select(max_fd + 1, &rfds, NULL, NULL, &tv) <= 0) - break; - - // Now check who has data pending in the tap - for (vnet = VirtIONetHead; vnet; vnet = vnet->next) { - - if (!FD_ISSET(vnet->tap_fd, &rfds)) - continue; - - if (virtqueue_pop(vnet->rx_vq, &elem) == 0) { - vnet->can_receive = 0; - continue; - } - - hdr = (void *)elem.in_sg[0].iov_base; - hdr->flags = 0; - hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE; -again: - len = readv(vnet->tap_fd, &elem.in_sg[1], elem.in_num - 1); - if (len == -1) { - if (errno == EINTR || errno == EAGAIN) - goto again; - else - fprintf(stderr, "reading network error %d", len); - } - virtqueue_push(vnet->rx_vq, &elem, sizeof(*hdr) + len); - vnet->do_notify = 1; - } - - /* signal other side */ - did_notify = 0; - for (vnet = VirtIONetHead; vnet; vnet = vnet->next) - if (vnet->do_notify) { - virtio_notify(&vnet->vdev, vnet->rx_vq); - did_notify++; - } - if (!did_notify) - break; - } - -} - /* TX */ static void virtio_net_flush_tx(VirtIONet *n, VirtQueue *vq) { @@ -303,12 +215,6 @@ PCIDevice *virtio_net_init(PCIBus *bus, NICInfo *nd, int devfn) memcpy(n->mac, nd->macaddr, 6); n->vc = qemu_new_vlan_client(nd->vlan, virtio_net_receive, virtio_net_can_receive, n); - n->tap_fd = hack_around_tap(n->vc->vlan->first_client); - if (n->tap_fd != -1) { - n->next = VirtIONetHead; - //push the device on top of the list - VirtIONetHead = n; - } n->tx_timer = qemu_new_timer(vm_clock, virtio_net_tx_timer, n); n->tx_timer_active = 0; diff --git a/qemu/vl.c b/qemu/vl.c index bcf893f..b8ce485 100644 --- a/qemu/vl.c +++ b/qemu/vl.c @@ -3966,15 +3966,8 @@ typedef struct TAPState { VLANClientState *vc; int fd; char down_script[1024]; - int no_poll; } TAPState; -static int tap_read_poll(void *opaque) -{ - TAPState *s = opaque; - return (!s->no_poll); -} - static void tap_receive(void *opaque, const uint8_t *buf, int size) { TAPState *s = opaque; @@ -4008,22 +4001,6 @@ static void tap_send(void *opaque) } } -int hack_around_tap(void *opaque) -{ - VLANClientState *vc = opaque; - TAPState *ts = vc->opaque; - - if (vc->fd_read != tap_receive) - return -1; - - if (ts) { - ts->no_poll = 1; - return ts->fd; - } - - return -1; -} - /* fd support */ static TAPState *net_tap_fd_init(VLANState *vlan, int fd) @@ -4034,10 +4011,8 @@ static TAPState *net_tap_fd_init(VLANState *vlan, int fd) if (!s) return NULL; s->fd = fd; - s->no_poll = 0; - enable_sigio_timer(fd); s->vc = qemu_new_vlan_client(vlan, tap_receive, NULL, s); - qemu_set_fd_handler2(s->fd, tap_read_poll, tap_send, NULL, s); + qemu_set_fd_handler2(s->fd, NULL, tap_send, NULL, s); snprintf(s->vc->info_str, sizeof(s->vc->info_str), "tap: fd=%d", fd); return s; } @@ -7972,10 +7947,7 @@ void main_loop_wait(int timeout) slirp_select_poll(&rfds, &wfds, &xfds); } #endif - virtio_net_poll(); - qemu_aio_poll(); - if (vm_running) { qemu_run_timers(&active_timers[QEMU_TIMER_VIRTUAL], qemu_get_clock(vm_clock)); ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. 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