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Re: [Qemu-devel] [PATCH v4] virtio-net: enable configurable tx queue siz
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v4] virtio-net: enable configurable tx queue size |
Date: |
Mon, 3 Jul 2017 22:18:28 +0300 |
On Wed, Jun 28, 2017 at 10:37:59AM +0800, Wei Wang wrote:
> This patch enables the virtio-net tx queue size to be configurable
> between 256 (the default queue size) and 1024 by the user when the
> vhost-user backend is used.
>
> Currently, the maximum tx queue size for other backends is 512 due
> to the following limitations:
> - QEMU backend: the QEMU backend implementation in some cases may
> send 1024+1 iovs to writev.
> - Vhost_net backend: there are possibilities that the guest sends
> a vring_desc of memory which crosses a MemoryRegion thereby
> generating more than 1024 iovs after translation from guest-physical
> address in the backend.
>
> Signed-off-by: Wei Wang <address@hidden>
I was going to apply this, but run into a host of issues:
This segfaults:
$ ./x86_64-softmmu/qemu-system-x86_64 -device virtio-net,tx_queue_size=1024
Segmentation fault (core dumped)
I tried to tweak this code a bit to avoid the crash, and I run into a further
issue:
$ ./x86_64-softmmu/qemu-system-x86_64 -device virtio-net,tx_queue_size=1024
Bad ram offset aa49002
Aborted (core dumped)
the second issue is especially concerning.
> ---
> hw/net/virtio-net.c | 32 ++++++++++++++++++++++++++++++--
> include/hw/virtio/virtio-net.h | 1 +
> 2 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 91eddaf..a1fc0db 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -34,8 +34,11 @@
>
> /* previously fixed value */
> #define VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE 256
> +#define VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE 256
> +
> /* for now, only allow larger queues; with virtio-1, guest can downsize */
> #define VIRTIO_NET_RX_QUEUE_MIN_SIZE VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE
> +#define VIRTIO_NET_TX_QUEUE_MIN_SIZE VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE
>
> /*
> * Calculate the number of bytes up to and including the given 'field' of
> @@ -1508,15 +1511,18 @@ static void virtio_net_add_queue(VirtIONet *n, int
> index)
>
> n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
> virtio_net_handle_rx);
> +
> if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
> n->vqs[index].tx_vq =
> - virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
> + virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> + virtio_net_handle_tx_timer);
> n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> virtio_net_tx_timer,
> &n->vqs[index]);
> } else {
> n->vqs[index].tx_vq =
> - virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
> + virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> + virtio_net_handle_tx_bh);
> n->vqs[index].tx_bh = qemu_bh_new(virtio_net_tx_bh, &n->vqs[index]);
> }
>
> @@ -1927,6 +1933,17 @@ static void virtio_net_device_realize(DeviceState
> *dev, Error **errp)
> return;
> }
>
> + if (n->net_conf.tx_queue_size < VIRTIO_NET_TX_QUEUE_MIN_SIZE ||
> + n->net_conf.tx_queue_size > VIRTQUEUE_MAX_SIZE ||
> + !is_power_of_2(n->net_conf.tx_queue_size)) {
> + error_setg(errp, "Invalid tx_queue_size (= %" PRIu16 "), "
> + "must be a power of 2 between %d and %d",
> + n->net_conf.tx_queue_size, VIRTIO_NET_TX_QUEUE_MIN_SIZE,
> + VIRTQUEUE_MAX_SIZE);
> + virtio_cleanup(vdev);
> + return;
> + }
> +
> n->max_queues = MAX(n->nic_conf.peers.queues, 1);
> if (n->max_queues * 2 + 1 > VIRTIO_QUEUE_MAX) {
> error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
> @@ -1947,6 +1964,15 @@ static void virtio_net_device_realize(DeviceState
> *dev, Error **errp)
> error_report("Defaulting to \"bh\"");
> }
>
> + /*
> + * Currently, backends other than vhost-user don't support 1024 queue
> + * size.
> + */
> + if (n->net_conf.tx_queue_size == VIRTQUEUE_MAX_SIZE &&
I'd prefer >= here.
> + n->nic_conf.peers.ncs[0]->info->type !=
> NET_CLIENT_DRIVER_VHOST_USER) {
> + n->net_conf.tx_queue_size = VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE;
> + }
> +
> for (i = 0; i < n->max_queues; i++) {
> virtio_net_add_queue(n, i);
> }
> @@ -2106,6 +2132,8 @@ static Property virtio_net_properties[] = {
> DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
> DEFINE_PROP_UINT16("rx_queue_size", VirtIONet, net_conf.rx_queue_size,
> VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE),
> + DEFINE_PROP_UINT16("tx_queue_size", VirtIONet, net_conf.tx_queue_size,
> + VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE),
> DEFINE_PROP_UINT16("host_mtu", VirtIONet, net_conf.mtu, 0),
> DEFINE_PROP_BOOL("x-mtu-bypass-backend", VirtIONet, mtu_bypass_backend,
> true),
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 602b486..b81b6a4 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -36,6 +36,7 @@ typedef struct virtio_net_conf
> int32_t txburst;
> char *tx;
> uint16_t rx_queue_size;
> + uint16_t tx_queue_size;
> uint16_t mtu;
> } virtio_net_conf;
>
> --
> 2.7.4
- Re: [Qemu-devel] [PATCH v4] virtio-net: enable configurable tx queue size,
Michael S. Tsirkin <=