On Mon, 2011-01-31 at 23:19 +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 <mst@xxxxxxxxxx>
> ---
>
> Untested, I'll send a pull request later after
> some testing assuming we've resolved the
> command line comments to everyone's satisfaction.
>
> Changes since v1:
> added vhostforce to enable vhost for non-MSI guests
I'm still not thrilled with the errno hack. If this is really a generic
problem, we should better architect the set_guest_notifiers() callback,
the force option feels like a band-aide. I'm still curious if we can't
be more dynamic about how we setup the set_guest_notifiers() function
pointer so it only gets set if (force || msix_enabled()) and we can
limit some of the impact here to vhost. Thanks,
Alex
> hw/vhost.c | 16 +++++++++++-----
> hw/vhost.h | 3 ++-
> hw/vhost_net.c | 8 +++++---
> hw/vhost_net.h | 2 +-
> hw/virtio-net.c | 6 ++++--
> hw/virtio-pci.c | 6 +++++-
> hw/virtio.h | 4 +++-
> net/tap.c | 6 ++++--
> qemu-options.hx | 4 +++-
> 9 files changed, 38 insertions(+), 17 deletions(-)
>
> diff --git a/hw/vhost.c b/hw/vhost.c
> index 6082da2..72df75f 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;
> @@ -636,9 +637,12 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
> goto fail;
> }
>
> - r = vdev->binding->set_guest_notifiers(vdev->binding_opaque, true);
> + r = vdev->binding->set_guest_notifiers(vdev->binding_opaque, true,
> + hdev->force);
> if (r < 0) {
> - fprintf(stderr, "Error binding guest notifier: %d\n", -r);
> + if (r != -EVIRTIO_DISABLED) {
> + fprintf(stderr, "Error binding guest notifier: %d\n", -r);
> + }
> goto fail_notifiers;
> }
>
> @@ -686,7 +690,8 @@ fail_vq:
> }
> fail_mem:
> fail_features:
> - vdev->binding->set_guest_notifiers(vdev->binding_opaque, false);
> + vdev->binding->set_guest_notifiers(vdev->binding_opaque, false,
> + hdev->force);
> fail_notifiers:
> fail:
> return r;
> @@ -704,7 +709,8 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
> }
> vhost_client_sync_dirty_bitmap(&hdev->client, 0,
> (target_phys_addr_t)~0x0ull);
> - r = vdev->binding->set_guest_notifiers(vdev->binding_opaque, false);
> + r = vdev->binding->set_guest_notifiers(vdev->binding_opaque, false,
> + hdev->force);
> if (r < 0) {
> fprintf(stderr, "vhost guest notifier cleanup failed: %d\n", r);
> fflush(stderr);
> diff --git a/hw/vhost.h b/hw/vhost.h
> index 86dd834..d5d4d86 100644
> --- a/hw/vhost.h
> +++ b/hw/vhost.h
> @@ -38,9 +38,10 @@ 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);
> 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..4f57271 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;
> }
> @@ -188,7 +189,8 @@ 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;
> }
> diff --git a/hw/vhost_net.h b/hw/vhost_net.h
> index 6c18ff7..8435094 100644
> --- a/hw/vhost_net.h
> +++ b/hw/vhost_net.h
> @@ -6,7 +6,7 @@
> 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);
>
> 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..5de3fee 100644
> --- a/hw/virtio-net.c
> +++ b/hw/virtio-net.c
> @@ -121,8 +121,10 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status)
> if (!n->vhost_started) {
> int 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);
> + if (r != -EVIRTIO_DISABLED) {
> + error_report("unable to start vhost net: %d: "
> + "falling back on userspace virtio", -r);
> + }
> } else {
> n->vhost_started = 1;
> }
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index d07ff97..c93ef11 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -595,12 +595,16 @@ static int virtio_pci_set_guest_notifier(void *opaque, int n, bool assign)
> return 0;
> }
>
> -static int virtio_pci_set_guest_notifiers(void *opaque, bool assign)
> +static int virtio_pci_set_guest_notifiers(void *opaque, bool assign, bool force)
> {
> VirtIOPCIProxy *proxy = opaque;
> VirtIODevice *vdev = proxy->vdev;
> int r, n;
>
> + if (assign && !force && !msix_enabled(&proxy->pci_dev)) {
> + return -EVIRTIO_DISABLED;
> + }
> +
> for (n = 0; n < VIRTIO_PCI_QUEUE_MAX; n++) {
> if (!virtio_queue_get_num(vdev, n)) {
> break;
> diff --git a/hw/virtio.h b/hw/virtio.h
> index d8546d5..156c9a3 100644
> --- a/hw/virtio.h
> +++ b/hw/virtio.h
> @@ -93,11 +93,13 @@ typedef struct {
> int (*load_config)(void * opaque, QEMUFile *f);
> int (*load_queue)(void * opaque, int n, QEMUFile *f);
> unsigned (*get_features)(void * opaque);
> - int (*set_guest_notifiers)(void * opaque, bool assigned);
> + int (*set_guest_notifiers)(void * opaque, bool assigned, bool force);
> int (*set_host_notifier)(void * opaque, int n, bool assigned);
> void (*vmstate_change)(void * opaque, bool running);
> } VirtIOBindings;
>
> +#define EVIRTIO_DISABLED ERANGE
> +
> #define VIRTIO_PCI_QUEUE_MAX 64
>
> #define VIRTIO_NO_VECTOR 0xffff
> 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"
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