On Tue, Jan 5, 2021 at 8:12 AM Yuri Benditovich <yuri.benditovich@xxxxxxxxxx> wrote: > > Existing TUN module is able to use provided "steering eBPF" to > calculate per-packet hash and derive the destination queue to > place the packet to. The eBPF uses mapped configuration data > containing a key for hash calculation and indirection table > with array of queues' indices. > > This series of patches adds support for virtio-net hash reporting > feature as defined in virtio specification. It extends the TUN module > and the "steering eBPF" as follows: > > Extended steering eBPF calculates the hash value and hash type, keeps > hash value in the skb->hash and returns index of destination virtqueue > and the type of the hash. TUN module keeps returned hash type in > (currently unused) field of the skb. > skb->__unused renamed to 'hash_report_type'. > > When TUN module is called later to allocate and fill the virtio-net > header and push it to destination virtqueue it populates the hash > and the hash type into virtio-net header. > > VHOST driver is made aware of respective virtio-net feature that > extends the virtio-net header to report the hash value and hash report > type. > > Yuri Benditovich (7): > skbuff: define field for hash report type > vhost: support for hash report virtio-net feature > tun: allow use of BPF_PROG_TYPE_SCHED_CLS program type > tun: free bpf_program by bpf_prog_put instead of bpf_prog_destroy > tun: add ioctl code TUNSETHASHPOPULATION > tun: populate hash in virtio-net header when needed > tun: report new tun feature IFF_HASH Patch 1/7 is missing. Skbuff fields are in short supply. I don't think we need to add one just for this narrow path entirely internal to the tun device. Instead, you could just run the flow_dissector in tun_put_user if the feature is negotiated. Indeed, the flow dissector seems more apt to me than BPF here. Note that the flow dissector internally can be overridden by a BPF program if the admin so chooses. This also hits on a deeper point with the choice of hash values, that I also noticed in my RFC patchset to implement the inverse [1][2]. It is much more detailed than skb->hash + skb->l4_hash currently offers, and that can be gotten for free from most hardware. In most practical cases, that information suffices. I added less specific fields VIRTIO_NET_HASH_REPORT_L4, VIRTIO_NET_HASH_REPORT_OTHER that work without explicit flow dissection. I understand that the existing fields are part of the standard. Just curious, what is their purpose beyond 4-tuple based flow hashing? [1] https://patchwork.kernel.org/project/netdevbpf/list/?series=406859&state=* [2] https://github.com/wdebruij/linux/commit/0f77febf22cd6ffc242a575807fa8382a26e511e
