[Qemu-devel] Re: [PATCHv3 0.14] vhost: force vhost off for non-MSI guests

[Alex Williamson]

On Tue, 2011-02-01 at 22:13 +0200, Michael S. Tsirkin wrote:
> When MSI is off, each interrupt needs to be bounced through the io
> thread when it's set/cleared, so vhost-net causes more context switches and
> higher CPU utilization than userspace virtio which handles networking in
> the same thread.
> 
> We'll need to fix this by adding level irq support in kvm irqfd,
> for now disable vhost-net in these configurations.
> 
> Added a vhostforce flag to force vhost-net back on.
> 
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
> 
> OK this is 0.14 material so quick review would be appreciated.
> This version's compiled only, I'll naturally test more before I
> queue it.
> 
> Changes from v2:
>       get rid of EVIRTIO, add a separate API to query
>       for fast guest notifiers

I like this better.  Thanks,

Alex

> Changes from v1:
>       add vhostforce flag
> 
>  hw/vhost.c      |   10 +++++++++-
>  hw/vhost.h      |    4 +++-
>  hw/vhost_net.c  |   24 ++++++++++++++++++------
>  hw/vhost_net.h  |    3 ++-
>  hw/virtio-net.c |    6 +++++-
>  hw/virtio-pci.c |    7 +++++++
>  hw/virtio.h     |    1 +
>  net/tap.c       |    6 ++++--
>  qemu-options.hx |    4 +++-
>  9 files changed, 52 insertions(+), 13 deletions(-)
> 
> diff --git a/hw/vhost.c b/hw/vhost.c
> index 6082da2..38cc3b3 100644
> --- a/hw/vhost.c
> +++ b/hw/vhost.c
> @@ -581,7 +581,7 @@ static void vhost_virtqueue_cleanup(struct vhost_dev *dev,
>                                0, virtio_queue_get_desc_size(vdev, idx));
>  }
>  
> -int vhost_dev_init(struct vhost_dev *hdev, int devfd)
> +int vhost_dev_init(struct vhost_dev *hdev, int devfd, bool force)
>  {
>      uint64_t features;
>      int r;
> @@ -613,6 +613,7 @@ int vhost_dev_init(struct vhost_dev *hdev, int devfd)
>      hdev->log_enabled = false;
>      hdev->started = false;
>      cpu_register_phys_memory_client(&hdev->client);
> +    hdev->force = force;
>      return 0;
>  fail:
>      r = -errno;
> @@ -627,6 +628,13 @@ void vhost_dev_cleanup(struct vhost_dev *hdev)
>      close(hdev->control);
>  }
>  
> +bool vhost_dev_query(struct vhost_dev *hdev, VirtIODevice *vdev)
> +{
> +    return !vdev->binding->query_guest_notifiers ||
> +        vdev->binding->query_guest_notifiers(vdev->binding_opaque) ||
> +        hdev->force;
> +}
> +
>  int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
>  {
>      int i, r;
> diff --git a/hw/vhost.h b/hw/vhost.h
> index 86dd834..c8c595a 100644
> --- a/hw/vhost.h
> +++ b/hw/vhost.h
> @@ -38,10 +38,12 @@ struct vhost_dev {
>      bool log_enabled;
>      vhost_log_chunk_t *log;
>      unsigned long long log_size;
> +    bool force;
>  };
>  
> -int vhost_dev_init(struct vhost_dev *hdev, int devfd);
> +int vhost_dev_init(struct vhost_dev *hdev, int devfd, bool force);
>  void vhost_dev_cleanup(struct vhost_dev *hdev);
> +bool vhost_dev_query(struct vhost_dev *hdev, VirtIODevice *vdev);
>  int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev);
>  void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev);
>  
> diff --git a/hw/vhost_net.c b/hw/vhost_net.c
> index c068be1..420e05f 100644
> --- a/hw/vhost_net.c
> +++ b/hw/vhost_net.c
> @@ -81,7 +81,8 @@ static int vhost_net_get_fd(VLANClientState *backend)
>      }
>  }
>  
> -struct vhost_net *vhost_net_init(VLANClientState *backend, int devfd)
> +struct vhost_net *vhost_net_init(VLANClientState *backend, int devfd,
> +                                 bool force)
>  {
>      int r;
>      struct vhost_net *net = qemu_malloc(sizeof *net);
> @@ -98,7 +99,7 @@ struct vhost_net *vhost_net_init(VLANClientState *backend, 
> int devfd)
>          (1 << VHOST_NET_F_VIRTIO_NET_HDR);
>      net->backend = r;
>  
> -    r = vhost_dev_init(&net->dev, devfd);
> +    r = vhost_dev_init(&net->dev, devfd, force);
>      if (r < 0) {
>          goto fail;
>      }
> @@ -121,6 +122,11 @@ fail:
>      return NULL;
>  }
>  
> +bool vhost_net_query(VHostNetState *net, VirtIODevice *dev)
> +{
> +    return vhost_dev_query(&net->dev, dev);
> +}
> +
>  int vhost_net_start(struct vhost_net *net,
>                      VirtIODevice *dev)
>  {
> @@ -188,15 +194,21 @@ void vhost_net_cleanup(struct vhost_net *net)
>      qemu_free(net);
>  }
>  #else
> -struct vhost_net *vhost_net_init(VLANClientState *backend, int devfd)
> +struct vhost_net *vhost_net_init(VLANClientState *backend, int devfd,
> +                                 bool force)
> +{
> +    return NULL;
> +}
> +
> +bool vhost_net_query(VHostNetState *net, VirtIODevice *dev)
>  {
> -     return NULL;
> +    return false;
>  }
>  
>  int vhost_net_start(struct vhost_net *net,
>                   VirtIODevice *dev)
>  {
> -     return -ENOSYS;
> +    return -ENOSYS;
>  }
>  void vhost_net_stop(struct vhost_net *net,
>                   VirtIODevice *dev)
> @@ -209,7 +221,7 @@ void vhost_net_cleanup(struct vhost_net *net)
>  
>  unsigned vhost_net_get_features(struct vhost_net *net, unsigned features)
>  {
> -     return features;
> +    return features;
>  }
>  void vhost_net_ack_features(struct vhost_net *net, unsigned features)
>  {
> diff --git a/hw/vhost_net.h b/hw/vhost_net.h
> index 6c18ff7..91e40b1 100644
> --- a/hw/vhost_net.h
> +++ b/hw/vhost_net.h
> @@ -6,8 +6,9 @@
>  struct vhost_net;
>  typedef struct vhost_net VHostNetState;
>  
> -VHostNetState *vhost_net_init(VLANClientState *backend, int devfd);
> +VHostNetState *vhost_net_init(VLANClientState *backend, int devfd, bool 
> force);
>  
> +bool vhost_net_query(VHostNetState *net, VirtIODevice *dev);
>  int vhost_net_start(VHostNetState *net, VirtIODevice *dev);
>  void vhost_net_stop(VHostNetState *net, VirtIODevice *dev);
>  
> diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> index ccb3e63..16ac103 100644
> --- a/hw/virtio-net.c
> +++ b/hw/virtio-net.c
> @@ -119,7 +119,11 @@ static void virtio_net_vhost_status(VirtIONet *n, 
> uint8_t status)
>          return;
>      }
>      if (!n->vhost_started) {
> -        int r = vhost_net_start(tap_get_vhost_net(n->nic->nc.peer), 
> &n->vdev);
> +        int r;
> +        if (!vhost_net_query(tap_get_vhost_net(n->nic->nc.peer), &n->vdev)) {
> +            return;
> +        }
> +        r = vhost_net_start(tap_get_vhost_net(n->nic->nc.peer), &n->vdev);
>          if (r < 0) {
>              error_report("unable to start vhost net: %d: "
>                           "falling back on userspace virtio", -r);
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index d07ff97..3911b09 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -595,6 +595,12 @@ static int virtio_pci_set_guest_notifier(void *opaque, 
> int n, bool assign)
>      return 0;
>  }
>  
> +static bool virtio_pci_query_guest_notifiers(void *opaque)
> +{
> +    VirtIOPCIProxy *proxy = opaque;
> +    return msix_enabled(&proxy->pci_dev);
> +}
> +
>  static int virtio_pci_set_guest_notifiers(void *opaque, bool assign)
>  {
>      VirtIOPCIProxy *proxy = opaque;
> @@ -658,6 +664,7 @@ static const VirtIOBindings virtio_pci_bindings = {
>      .save_queue = virtio_pci_save_queue,
>      .load_queue = virtio_pci_load_queue,
>      .get_features = virtio_pci_get_features,
> +    .query_guest_notifiers = virtio_pci_query_guest_notifiers,
>      .set_host_notifier = virtio_pci_set_host_notifier,
>      .set_guest_notifiers = virtio_pci_set_guest_notifiers,
>      .vmstate_change = virtio_pci_vmstate_change,
> diff --git a/hw/virtio.h b/hw/virtio.h
> index d8546d5..31d16e1 100644
> --- a/hw/virtio.h
> +++ b/hw/virtio.h
> @@ -93,6 +93,7 @@ typedef struct {
>      int (*load_config)(void * opaque, QEMUFile *f);
>      int (*load_queue)(void * opaque, int n, QEMUFile *f);
>      unsigned (*get_features)(void * opaque);
> +    bool (*query_guest_notifiers)(void * opaque);
>      int (*set_guest_notifiers)(void * opaque, bool assigned);
>      int (*set_host_notifier)(void * opaque, int n, bool assigned);
>      void (*vmstate_change)(void * opaque, bool running);
> diff --git a/net/tap.c b/net/tap.c
> index eada34a..b8cd252 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -491,8 +491,10 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const 
> char *name, VLANState *vlan
>          }
>      }
>  
> -    if (qemu_opt_get_bool(opts, "vhost", !!qemu_opt_get(opts, "vhostfd"))) {
> +    if (qemu_opt_get_bool(opts, "vhost", !!qemu_opt_get(opts, "vhostfd") ||
> +                          qemu_opt_get_bool(opts, "vhostforce", false))) {
>          int vhostfd, r;
> +        bool force = qemu_opt_get_bool(opts, "vhostforce", false);
>          if (qemu_opt_get(opts, "vhostfd")) {
>              r = net_handle_fd_param(mon, qemu_opt_get(opts, "vhostfd"));
>              if (r == -1) {
> @@ -502,7 +504,7 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char 
> *name, VLANState *vlan
>          } else {
>              vhostfd = -1;
>          }
> -        s->vhost_net = vhost_net_init(&s->nc, vhostfd);
> +        s->vhost_net = vhost_net_init(&s->nc, vhostfd, force);
>          if (!s->vhost_net) {
>              error_report("vhost-net requested but could not be initialized");
>              return -1;
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 898561d..11c93a2 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1050,7 +1050,7 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>      "-net tap[,vlan=n][,name=str],ifname=name\n"
>      "                connect the host TAP network interface to VLAN 'n'\n"
>  #else
> -    "-net 
> tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h]\n"
> +    "-net 
> tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
>      "                connect the host TAP network interface to VLAN 'n' and 
> use the\n"
>      "                network scripts 'file' (default=" 
> DEFAULT_NETWORK_SCRIPT ")\n"
>      "                and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
> @@ -1061,6 +1061,8 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>      "                use vnet_hdr=off to avoid enabling the IFF_VNET_HDR tap 
> flag\n"
>      "                use vnet_hdr=on to make the lack of IFF_VNET_HDR 
> support an error condition\n"
>      "                use vhost=on to enable experimental in kernel 
> accelerator\n"
> +    "                    (only has effect for virtio guests which use 
> MSIX)\n"
> +    "                use vhostforce=on to force vhost on for non-MSIX virtio 
> guests\n"
>      "                use 'vhostfd=h' to connect to an already opened vhost 
> net device\n"
>  #endif
>      "-net 
> socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"