Re: [Qemu-devel] [PATCH V3] tap: vhost busy polling support

[Jason Wang <jasowang@redhat.com>]

On 2016年05月31日 02:07, Michael S. Tsirkin wrote:
> On Thu, Apr 07, 2016 at 12:56:24PM +0800, Jason Wang wrote:
>> This patch add the capability of basic vhost net busy polling which is
>> supported by recent kernel. User could configure the maximum number of
>> us that could be spent on busy polling through a new property of tap
>> "vhost-poll-us".
> I applied this but now I had a thought - should we generalize this to
> "poll-us"? Down the road tun could support busy olling just like
> sockets do.

Looks two different things. Socket busy polling depends on the value set 
by sysctl or SO_BUSY_POLL, which should be transparent to qemu.

>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>   hw/net/vhost_net.c                |  2 +-
>>   hw/scsi/vhost-scsi.c              |  2 +-
>>   hw/virtio/vhost-backend.c         |  8 ++++++++
>>   hw/virtio/vhost.c                 | 40 ++++++++++++++++++++++++++++++++++++++-
>>   include/hw/virtio/vhost-backend.h |  3 +++
>>   include/hw/virtio/vhost.h         |  3 ++-
>>   include/net/vhost_net.h           |  1 +
>>   net/tap.c                         | 10 ++++++++--
>>   net/vhost-user.c                  |  1 +
>>   qapi-schema.json                  |  6 +++++-
>>   qemu-options.hx                   |  3 +++
>>   11 files changed, 72 insertions(+), 7 deletions(-)
>>
>> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
>> index 6e1032f..1840c73 100644
>> --- a/hw/net/vhost_net.c
>> +++ b/hw/net/vhost_net.c
>> @@ -166,7 +166,7 @@ struct vhost_net *vhost_net_init(VhostNetOptions *options)
>>       }
>>   
>>       r = vhost_dev_init(&net->dev, options->opaque,
>> -                       options->backend_type);
>> +                       options->backend_type, options->busyloop_timeout);
>>       if (r < 0) {
>>           goto fail;
>>       }
>> diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
>> index 9261d51..2a00f2f 100644
>> --- a/hw/scsi/vhost-scsi.c
>> +++ b/hw/scsi/vhost-scsi.c
>> @@ -248,7 +248,7 @@ static void vhost_scsi_realize(DeviceState *dev, Error **errp)
>>       s->dev.backend_features = 0;
>>   
>>       ret = vhost_dev_init(&s->dev, (void *)(uintptr_t)vhostfd,
>> -                         VHOST_BACKEND_TYPE_KERNEL);
>> +                         VHOST_BACKEND_TYPE_KERNEL, 0);
>>       if (ret < 0) {
>>           error_setg(errp, "vhost-scsi: vhost initialization failed: %s",
>>                      strerror(-ret));
>> diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
>> index b358902..d62372e 100644
>> --- a/hw/virtio/vhost-backend.c
>> +++ b/hw/virtio/vhost-backend.c
>> @@ -138,6 +138,12 @@ static int vhost_kernel_set_vring_call(struct vhost_dev *dev,
>>       return vhost_kernel_call(dev, VHOST_SET_VRING_CALL, file);
>>   }
>>   
>> +static int vhost_kernel_set_vring_busyloop_timeout(struct vhost_dev *dev,
>> +                                                   struct vhost_vring_state *s)
>> +{
>> +    return vhost_kernel_call(dev, VHOST_SET_VRING_BUSYLOOP_TIMEOUT, s);
>> +}
>> +
>>   static int vhost_kernel_set_features(struct vhost_dev *dev,
>>                                        uint64_t features)
>>   {
>> @@ -185,6 +191,8 @@ static const VhostOps kernel_ops = {
>>           .vhost_get_vring_base = vhost_kernel_get_vring_base,
>>           .vhost_set_vring_kick = vhost_kernel_set_vring_kick,
>>           .vhost_set_vring_call = vhost_kernel_set_vring_call,
>> +        .vhost_set_vring_busyloop_timeout =
>> +                                vhost_kernel_set_vring_busyloop_timeout,
>>           .vhost_set_features = vhost_kernel_set_features,
>>           .vhost_get_features = vhost_kernel_get_features,
>>           .vhost_set_owner = vhost_kernel_set_owner,
>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>> index 4400718..ebf8b08 100644
>> --- a/hw/virtio/vhost.c
>> +++ b/hw/virtio/vhost.c
>> @@ -964,6 +964,28 @@ static void vhost_eventfd_del(MemoryListener *listener,
>>   {
>>   }
>>   
>> +static int vhost_virtqueue_set_busyloop_timeout(struct vhost_dev *dev,
>> +                                                int n, uint32_t timeout)
>> +{
>> +    int vhost_vq_index = dev->vhost_ops->vhost_get_vq_index(dev, n);
>> +    struct vhost_vring_state state = {
>> +        .index = vhost_vq_index,
>> +        .num = timeout,
>> +    };
>> +    int r;
>> +
>> +    if (!dev->vhost_ops->vhost_set_vring_busyloop_timeout) {
>> +        return -EINVAL;
>> +    }
>> +
>> +    r = dev->vhost_ops->vhost_set_vring_busyloop_timeout(dev, &state);
>> +    if (r) {
>> +        return r;
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   static int vhost_virtqueue_init(struct vhost_dev *dev,
>>                                   struct vhost_virtqueue *vq, int n)
>>   {
>> @@ -994,7 +1016,7 @@ static void vhost_virtqueue_cleanup(struct vhost_virtqueue *vq)
>>   }
>>   
>>   int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>> -                   VhostBackendType backend_type)
>> +                   VhostBackendType backend_type, uint32_t busyloop_timeout)
>>   {
>>       uint64_t features;
>>       int i, r;
>> @@ -1035,6 +1057,17 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>>               goto fail_vq;
>>           }
>>       }
>> +
>> +    if (busyloop_timeout) {
>> +        for (i = 0; i < hdev->nvqs; ++i) {
>> +            r = vhost_virtqueue_set_busyloop_timeout(hdev, hdev->vq_index + i,
>> +                                                     busyloop_timeout);
>> +            if (r < 0) {
>> +                goto fail_busyloop;
>> +            }
>> +        }
>> +    }
>> +
>>       hdev->features = features;
>>   
>>       hdev->memory_listener = (MemoryListener) {
>> @@ -1077,6 +1110,11 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>>       hdev->memory_changed = false;
>>       memory_listener_register(&hdev->memory_listener, &address_space_memory);
>>       return 0;
>> +fail_busyloop:
>> +    while (--i >= 0) {
>> +        vhost_virtqueue_set_busyloop_timeout(hdev, hdev->vq_index + i, 0);
>> +    }
>> +    i = hdev->nvqs;
>>   fail_vq:
>>       while (--i >= 0) {
>>           vhost_virtqueue_cleanup(hdev->vqs + i);
>> diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
>> index 95fcc96..84e1cb7 100644
>> --- a/include/hw/virtio/vhost-backend.h
>> +++ b/include/hw/virtio/vhost-backend.h
>> @@ -57,6 +57,8 @@ typedef int (*vhost_set_vring_kick_op)(struct vhost_dev *dev,
>>                                          struct vhost_vring_file *file);
>>   typedef int (*vhost_set_vring_call_op)(struct vhost_dev *dev,
>>                                          struct vhost_vring_file *file);
>> +typedef int (*vhost_set_vring_busyloop_timeout_op)(struct vhost_dev *dev,
>> +                                                   struct vhost_vring_state *r);
>>   typedef int (*vhost_set_features_op)(struct vhost_dev *dev,
>>                                        uint64_t features);
>>   typedef int (*vhost_get_features_op)(struct vhost_dev *dev,
>> @@ -91,6 +93,7 @@ typedef struct VhostOps {
>>       vhost_get_vring_base_op vhost_get_vring_base;
>>       vhost_set_vring_kick_op vhost_set_vring_kick;
>>       vhost_set_vring_call_op vhost_set_vring_call;
>> +    vhost_set_vring_busyloop_timeout_op vhost_set_vring_busyloop_timeout;
>>       vhost_set_features_op vhost_set_features;
>>       vhost_get_features_op vhost_get_features;
>>       vhost_set_owner_op vhost_set_owner;
>> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
>> index b60d758..2106ed8 100644
>> --- a/include/hw/virtio/vhost.h
>> +++ b/include/hw/virtio/vhost.h
>> @@ -64,7 +64,8 @@ struct vhost_dev {
>>   };
>>   
>>   int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>> -                   VhostBackendType backend_type);
>> +                   VhostBackendType backend_type,
>> +                   uint32_t busyloop_timeout);
>>   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/include/net/vhost_net.h b/include/net/vhost_net.h
>> index 3389b41..8354b98 100644
>> --- a/include/net/vhost_net.h
>> +++ b/include/net/vhost_net.h
>> @@ -10,6 +10,7 @@ typedef struct vhost_net VHostNetState;
>>   typedef struct VhostNetOptions {
>>       VhostBackendType backend_type;
>>       NetClientState *net_backend;
>> +    uint32_t busyloop_timeout;
>>       void *opaque;
>>   } VhostNetOptions;
>>   
>> diff --git a/net/tap.c b/net/tap.c
>> index 740e8a2..7e28102 100644
>> --- a/net/tap.c
>> +++ b/net/tap.c
>> @@ -663,6 +663,11 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
>>   
>>           options.backend_type = VHOST_BACKEND_TYPE_KERNEL;
>>           options.net_backend = &s->nc;
>> +        if (tap->has_vhost_poll_us) {
>> +            options.busyloop_timeout = tap->vhost_poll_us;
>> +        } else {
>> +            options.busyloop_timeout = 0;
>> +        }
>>   
>>           if (vhostfdname) {
>>               vhostfd = monitor_fd_param(cur_mon, vhostfdname, &err);
>> @@ -686,8 +691,9 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
>>                          "vhost-net requested but could not be initialized");
>>               return;
>>           }
>> -    } else if (vhostfdname) {
>> -        error_setg(errp, "vhostfd= is not valid without vhost");
>> +    } else if (vhostfdname || tap->has_vhost_poll_us) {
>> +        error_setg(errp, "vhostfd(s)= or vhost_poll_us= is not valid"
>> +                         " without vhost");
>>       }
>>   }
>>   
>> diff --git a/net/vhost-user.c b/net/vhost-user.c
>> index 1b9e73a..b200182 100644
>> --- a/net/vhost-user.c
>> +++ b/net/vhost-user.c
>> @@ -80,6 +80,7 @@ static int vhost_user_start(int queues, NetClientState *ncs[])
>>   
>>           options.net_backend = ncs[i];
>>           options.opaque      = s->chr;
>> +        options.busyloop_timeout = 0;
>>           s->vhost_net = vhost_net_init(&options);
>>           if (!s->vhost_net) {
>>               error_report("failed to init vhost_net for queue %d", i);
>> diff --git a/qapi-schema.json b/qapi-schema.json
>> index 54634c4..8afdedf 100644
>> --- a/qapi-schema.json
>> +++ b/qapi-schema.json
>> @@ -2531,6 +2531,9 @@
>>   #
>>   # @queues: #optional number of queues to be created for multiqueue capable tap
>>   #
>> +# @vhost-poll-us: #optional maximum number of microseconds that could
>> +# be spent on busy polling for vhost net (since 2.7)
>> +#
>>   # Since 1.2
>>   ##
>>   { 'struct': 'NetdevTapOptions',
>> @@ -2547,7 +2550,8 @@
>>       '*vhostfd':    'str',
>>       '*vhostfds':   'str',
>>       '*vhostforce': 'bool',
>> -    '*queues':     'uint32'} }
>> +    '*queues':     'uint32',
>> +    '*vhost-poll-us': 'uint32'} }
>>   
>>   ##
>>   # @NetdevSocketOptions
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index 587de8f..22ddb82 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -1569,6 +1569,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>>       "-netdev tap,id=str[,fd=h][,fds=x:y:...:z][,ifname=name][,script=file][,downscript=dfile]\n"
>>       "         [,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off]\n"
>>       "         [,vhostfd=h][,vhostfds=x:y:...:z][,vhostforce=on|off][,queues=n]\n"
>> +    "         [,vhost-poll-us=n]\n"
>>       "                configure a host TAP network backend with ID 'str'\n"
>>       "                use network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
>>       "                to configure it and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
>> @@ -1588,6 +1589,8 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>>       "                use 'vhostfd=h' to connect to an already opened vhost net device\n"
>>       "                use 'vhostfds=x:y:...:z to connect to multiple already opened vhost net devices\n"
>>       "                use 'queues=n' to specify the number of queues to be created for multiqueue TAP\n"
>> +    "                use 'vhost-poll-us=n' to speciy the maximum number of microseconds that could be\n"
>> +    "                spent on busy polling for vhost net\n"
>>       "-netdev bridge,id=str[,br=bridge][,helper=helper]\n"
>>       "                configure a host TAP network backend with ID 'str' that is\n"
>>       "                connected to a bridge (default=" DEFAULT_BRIDGE_INTERFACE ")\n"
>> -- 
>> 2.5.0