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

[Jason Wang <jasowang@redhat.com>]

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.


> +    uint64_t ret = features;
> +#ifndef CONFIG_EBPF
> +    virtio_clear_feature(&ret, VIRTIO_NET_F_RSS);
> +#endif
> +    /* for now, there is no solution for populating the hash from eBPF */
> +    virtio_clear_feature(&ret, VIRTIO_NET_F_HASH_REPORT);
> +
> +    return ret;
> +}
> +
>   static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
>                                           Error **errp)
>   {
> @@ -725,9 +738,9 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
>           return features;
>       }
>   
> -    virtio_clear_feature(&features, VIRTIO_NET_F_RSS);
> -    virtio_clear_feature(&features, VIRTIO_NET_F_HASH_REPORT);
> -    features = vhost_net_get_features(get_vhost_net(nc->peer), features);
> +    features = fix_ebpf_vhost_features(
> +            vhost_net_get_features(get_vhost_net(nc->peer), features));
> +
>       vdev->backend_features = features;
>   
>       if (n->mtu_bypass_backend &&
> @@ -1151,12 +1164,79 @@ static int virtio_net_handle_announce(VirtIONet *n, uint8_t cmd,
>       }
>   }
>   
> +static void virtio_net_detach_epbf_rss(VirtIONet *n);
> +
>   static void virtio_net_disable_rss(VirtIONet *n)
>   {
>       if (n->rss_data.enabled) {
>           trace_virtio_net_rss_disable();
>       }
>       n->rss_data.enabled = false;
> +
> +    virtio_net_detach_epbf_rss(n);
> +}
> +
> +static bool virtio_net_attach_ebpf_to_backend(NICState *nic, int prog_fd)
> +{
> +    NetClientState *nc = qemu_get_peer(qemu_get_queue(nic), 0);
> +    if (nc == NULL || nc->info->set_steering_ebpf == NULL) {
> +        return false;
> +    }
> +
> +    return nc->info->set_steering_ebpf(nc, prog_fd);
> +}
> +
> +static void rss_data_to_rss_config(struct VirtioNetRssData *data,
> +                                   struct EBPFRSSConfig *config)
> +{
> +    config->redirect = data->redirect;
> +    config->populate_hash = data->populate_hash;
> +    config->hash_types = data->hash_types;
> +    config->indirections_len = data->indirections_len;
> +    config->default_queue = data->default_queue;
> +}
> +
> +static bool virtio_net_attach_epbf_rss(VirtIONet *n)
> +{
> +    struct EBPFRSSConfig config = {};
> +
> +    if (!ebpf_rss_is_loaded(&n->ebpf_rss)) {
> +        return false;
> +    }
> +
> +    rss_data_to_rss_config(&n->rss_data, &config);
> +
> +    if (!ebpf_rss_set_all(&n->ebpf_rss, &config,
> +                          n->rss_data.indirections_table, n->rss_data.key)) {
> +        return false;
> +    }
> +
> +    if (!virtio_net_attach_ebpf_to_backend(n->nic, n->ebpf_rss.program_fd)) {
> +        return false;
> +    }
> +
> +    return true;
> +}
> +
> +static void virtio_net_detach_epbf_rss(VirtIONet *n)
> +{
> +    virtio_net_attach_ebpf_to_backend(n->nic, -1);
> +}
> +
> +static bool virtio_net_load_ebpf(VirtIONet *n)
> +{
> +    if (!virtio_net_attach_ebpf_to_backend(n->nic, -1)) {
> +        /* backend does't support steering ebpf */
> +        return false;
> +    }
> +
> +    return ebpf_rss_load(&n->ebpf_rss);
> +}
> +
> +static void virtio_net_unload_ebpf(VirtIONet *n)
> +{
> +    virtio_net_attach_ebpf_to_backend(n->nic, -1);
> +    ebpf_rss_unload(&n->ebpf_rss);
>   }
>   
>   static uint16_t virtio_net_handle_rss(VirtIONet *n,
> @@ -1271,6 +1351,25 @@ static uint16_t virtio_net_handle_rss(VirtIONet *n,
>           goto error;
>       }
>       n->rss_data.enabled = true;
> +
> +    if (!n->rss_data.populate_hash) {
> +        if (!virtio_net_attach_epbf_rss(n)) {
> +            /* EBPF must be loaded for vhost */
> +            if (get_vhost_net(qemu_get_queue(n->nic)->peer)) {
> +                warn_report("Can't load eBPF RSS for vhost");
> +                goto error;


How about stop the vhost in this case?

Thanks