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

[Yuri Benditovich]

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.

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
>
>
> >
>