Re: [RFC PATCH v3 5/6] virtio-net: Added eBPF RSS to virtio-net.

[Yuri Benditovich]

On Sun, Jan 24, 2021 at 10:24 AM Yuri Benditovich
<yuri.benditovich@daynix.com> wrote:
>
> Hi Jason,
>
> I've prepared a POC of graceful switch to 'vhost off' if respective
> features are acked by the guest.
> Such a way we do not need to silently clear RSS and hash report
> features in case of 'vhost on'.
> Can you please review it and provide your feedback?
>
> I think the only open question is what to do with cases of vhost-user
> and vhost-vdpa.
>
> https://github.com/qemu/qemu/pull/105
> This pull request is for reviews only.

Unfortunately qemu github PR is closed for comments
This is the link to the same on Daynix repository

https://github.com/daynix/qemu/pull/1

>
> Thanks in advance
>
>
>
>
>
>
> On Mon, Jan 18, 2021 at 5:16 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> >
> > On 2021/1/17 下午5:04, Yuri Benditovich wrote:
> > > On Fri, Jan 15, 2021 at 9:20 AM Jason Wang<jasowang@redhat.com>  wrote:
> > >> On 2021/1/15 上午5:16, Andrew Melnychenko wrote:
> > >>> From: Andrew<andrew@daynix.com>
> > >>>
> > >>> When RSS is enabled the device tries to load the eBPF program
> > >>> to select RX virtqueue in the TUN. If eBPF can be loaded
> > >>> the RSS will function also with vhost (works with kernel 5.8 and later).
> > >>> Software RSS is used as a fallback with vhost=off when eBPF can't be 
> > >>> loaded
> > >>> or when hash population requested by the guest.
> > >>>
> > >>> Signed-off-by: Yuri Benditovich<yuri.benditovich@daynix.com>
> > >>> Signed-off-by: Andrew Melnychenko<andrew@daynix.com>
> > >>> ---
> > >>>    hw/net/vhost_net.c             |   2 +
> > >>>    hw/net/virtio-net.c            | 125 
> > >>> +++++++++++++++++++++++++++++++--
> > >>>    include/hw/virtio/virtio-net.h |   4 ++
> > >>>    net/vhost-vdpa.c               |   2 +
> > >>>    4 files changed, 129 insertions(+), 4 deletions(-)
> > >>>
> > >>> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> > >>> index 24d555e764..16124f99c3 100644
> > >>> --- a/hw/net/vhost_net.c
> > >>> +++ b/hw/net/vhost_net.c
> > >>> @@ -71,6 +71,8 @@ static const int user_feature_bits[] = {
> > >>>        VIRTIO_NET_F_MTU,
> > >>>        VIRTIO_F_IOMMU_PLATFORM,
> > >>>        VIRTIO_F_RING_PACKED,
> > >>> +    VIRTIO_NET_F_RSS,
> > >>> +    VIRTIO_NET_F_HASH_REPORT,
> > >>>
> > >>>        /* This bit implies RARP isn't sent by QEMU out of band */
> > >>>        VIRTIO_NET_F_GUEST_ANNOUNCE,
> > >>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > >>> index 09ceb02c9d..37016fc73a 100644
> > >>> --- a/hw/net/virtio-net.c
> > >>> +++ b/hw/net/virtio-net.c
> > >>> @@ -691,6 +691,19 @@ static void virtio_net_set_queues(VirtIONet *n)
> > >>>
> > >>>    static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue);
> > >>>
> > >>> +static uint64_t fix_ebpf_vhost_features(uint64_t features)
> > >>> +{
> > >>> +    /* If vhost=on & CONFIG_EBPF doesn't set - disable RSS feature */
> > >> I still think we should not clear feature silently. This may break
> > >> migraiton if the feature is cleared on destination.
> > > Do I understand it correctly that if we do not clear features silently
> > > and implement a graceful drop to vhost=off when we can't do what we
> > > need with vhost - then we do not need to add any migration blocker?
> >
> >
> > Yes. I think we won't go with migration blocker since we need support
> > migration in the end.
> >
> > Thanks
> >
> >
> > >
> >