On Tue, Jan 12, 2021 at 9:41 PM Yuri Benditovich
[off-list ref] 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.
Comment from Willem de Bruijn:
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
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
drivers/net/tun.c | 43 +++++++++++++++++++++++++++++++------
drivers/vhost/net.c | 37 ++++++++++++++++++++++++-------
include/linux/skbuff.h | 7 +++++-
include/uapi/linux/if_tun.h | 2 ++
4 files changed, 74 insertions(+), 15 deletions(-)
--
2.17.1
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