Re: [Qemu-devel] [ RFC Patch v4 1/3] virtio-net rsc: add a new host offload(rsc) feature bit

[Michael S. Tsirkin]

On Tue, Apr 05, 2016 at 10:05:17AM +0800, Jason Wang wrote:
> 
> 
> On 04/04/2016 03:25 AM, address@hidden wrote:
> > From: Wei Xu <address@hidden>
> >
> > A new feature bit 'VIRTIO_NET_F_GUEST_RSC' is introduced to support WHQL
> > Receive-Segment-Offload test, this feature will coalesce tcp packets in
> > IPv4/6 for userspace virtio-net driver.
> >
> > This feature can be enabled either by 'ACK' the feature when loading
> > the driver in the guest, or by sending the 
> > 'VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET'
> > command to the host via control queue.
> >
> > Signed-off-by: Wei Xu <address@hidden>
> > ---
> >  hw/net/virtio-net.c                         | 29 
> > +++++++++++++++++++++++++++--
> >  include/standard-headers/linux/virtio_net.h |  1 +
> >  2 files changed, 28 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > index 5798f87..bd91a4b 100644
> > --- a/hw/net/virtio-net.c
> > +++ b/hw/net/virtio-net.c
> > @@ -537,6 +537,7 @@ static uint64_t virtio_net_get_features(VirtIODevice 
> > *vdev, uint64_t features,
> >          virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_TSO4);
> >          virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_TSO6);
> >          virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ECN);
> > +        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_RSC);
> 
> Several questions here:
> 
> - I think RSC should work even without vnet_hdr?
> - Need we differentiate ipv4 and ipv6 like TSO here?
> - And looks like this patch should be squash to following patches.
> 
> >      }
> >  
> >      if (!peer_has_vnet_hdr(n) || !peer_has_ufo(n)) {
> > @@ -582,7 +583,8 @@ static uint64_t 
> > virtio_net_guest_offloads_by_features(uint32_t features)
> >          (1ULL << VIRTIO_NET_F_GUEST_TSO4) |
> >          (1ULL << VIRTIO_NET_F_GUEST_TSO6) |
> >          (1ULL << VIRTIO_NET_F_GUEST_ECN)  |
> > -        (1ULL << VIRTIO_NET_F_GUEST_UFO);
> > +        (1ULL << VIRTIO_NET_F_GUEST_UFO)  |
> > +        (1ULL << VIRTIO_NET_F_GUEST_RSC);
> 
> Looks like this is unnecessary since we won't set peer offload based on
> GUEST_RSC.
> 
> >  
> >      return guest_offloads_mask & features;
> >  }
> > @@ -1089,7 +1091,8 @@ static int receive_filter(VirtIONet *n, const uint8_t 
> > *buf, int size)
> >      return 0;
> >  }
> >  
> > -static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, 
> > size_t size)
> > +static ssize_t virtio_net_do_receive(NetClientState *nc,
> > +                                     const uint8_t *buf, size_t size)
> >  {
> >      VirtIONet *n = qemu_get_nic_opaque(nc);
> >      VirtIONetQueue *q = virtio_net_get_subqueue(nc);
> > @@ -1685,6 +1688,26 @@ static int virtio_net_load_device(VirtIODevice 
> > *vdev, QEMUFile *f,
> >      return 0;
> >  }
> >  
> > +
> > +static ssize_t virtio_net_rsc_receive(NetClientState *nc,
> > +                                      const uint8_t *buf, size_t size)
> > +{
> > +    return virtio_net_do_receive(nc, buf, size);
> > +}
> > +
> > +static ssize_t virtio_net_receive(NetClientState *nc,
> > +                                  const uint8_t *buf, size_t size)
> > +{
> > +    VirtIONet *n;
> > +
> > +    n = qemu_get_nic_opaque(nc);
> > +    if (n->curr_guest_offloads & VIRTIO_NET_F_GUEST_RSC) {
> > +        return virtio_net_rsc_receive(nc, buf, size);
> > +    } else {
> > +        return virtio_net_do_receive(nc, buf, size);
> > +    }
> > +}
> 
> The changes here looks odd since it did nothing. Like I've mentioned,
> better merge the patch into following ones.
> 
> > +
> >  static NetClientInfo net_virtio_info = {
> >      .type = NET_CLIENT_OPTIONS_KIND_NIC,
> >      .size = sizeof(NICState),
> > @@ -1909,6 +1932,8 @@ static Property virtio_net_properties[] = {
> >                         TX_TIMER_INTERVAL),
> >      DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST),
> >      DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
> > +    DEFINE_PROP_BIT("guest_rsc", VirtIONet, host_features,
> > +                    VIRTIO_NET_F_GUEST_RSC, true),
> 
> Need to compat the bit for old machine type to unbreak migration I believe?

And definitely disable by default.

> Btw, also need a patch for virtio spec.
> 
> Thanks
> 
> >      DEFINE_PROP_END_OF_LIST(),
> >  };
> >  
> > diff --git a/include/standard-headers/linux/virtio_net.h 
> > b/include/standard-headers/linux/virtio_net.h
> > index a78f33e..5b95762 100644
> > --- a/include/standard-headers/linux/virtio_net.h
> > +++ b/include/standard-headers/linux/virtio_net.h
> > @@ -55,6 +55,7 @@
> >  #define VIRTIO_NET_F_MQ    22      /* Device supports Receive Flow
> >                                      * Steering */
> >  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23      /* Set MAC address */
> > +#define VIRTIO_NET_F_GUEST_RSC  24      /* Guest can coalesce tcp packets 
> > */
> >  
> >  #ifndef VIRTIO_NET_NO_LEGACY
> >  #define VIRTIO_NET_F_GSO   6       /* Host handles pkts w/ any GSO type */