Re: [PATCH net-next v8 0/6] tun: Introduce virtio-net hashing feature

[Lei Yang]

QE tested this series of patches with virtio-net regression tests,
everything works fine.

Tested-by: Lei Yang <leiyang@xxxxxxxxxx>

On Thu, Mar 6, 2025 at 5:57 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
>
> virtio-net have two usage of hashes: one is RSS and another is hash
> reporting. Conventionally the hash calculation was done by the VMM.
> However, computing the hash after the queue was chosen defeats the
> purpose of RSS.
>
> Another approach is to use eBPF steering program. This approach has
> another downside: it cannot report the calculated hash due to the
> restrictive nature of eBPF.
>
> Introduce the code to compute hashes to the kernel in order to overcome
> thse challenges.
>
> An alternative solution is to extend the eBPF steering program so that it
> will be able to report to the userspace, but it is based on context
> rewrites, which is in feature freeze. We can adopt kfuncs, but they will
> not be UAPIs. We opt to ioctl to align with other relevant UAPIs (KVM
> and vhost_net).
>
> The patches for QEMU to use this new feature was submitted as RFC and
> is available at:
> https://patchew.org/QEMU/20240915-hash-v3-0-79cb08d28647@xxxxxxxxxx/
>
> This work was presented at LPC 2024:
> https://lpc.events/event/18/contributions/1963/
>
> V1 -> V2:
>   Changed to introduce a new BPF program type.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
> ---
> Changes in v8:
> - Disabled IPv6 to eliminate noises in tests.
> - Added a branch in tap to avoid unnecessary dissection when hash
>   reporting is disabled.
> - Removed unnecessary rtnl_lock().
> - Extracted code to handle new ioctls into separate functions to avoid
>   adding extra NULL checks to the code handling other ioctls.
> - Introduced variable named "fd" to __tun_chr_ioctl().
> - s/-/=/g in a patch message to avoid confusing Git.
> - Link to v7: https://lore.kernel.org/r/20250228-rss-v7-0-844205cbbdd6@xxxxxxxxxx
>
> Changes in v7:
> - Ensured to set hash_report to VIRTIO_NET_HASH_REPORT_NONE for
>   VHOST_NET_F_VIRTIO_NET_HDR.
> - s/4/sizeof(u32)/ in patch "virtio_net: Add functions for hashing".
> - Added tap_skb_cb type.
> - Rebased.
> - Link to v6: https://lore.kernel.org/r/20250109-rss-v6-0-b1c90ad708f6@xxxxxxxxxx
>
> Changes in v6:
> - Extracted changes to fill vnet header holes into another series.
> - Squashed patches "skbuff: Introduce SKB_EXT_TUN_VNET_HASH", "tun:
>   Introduce virtio-net hash reporting feature", and "tun: Introduce
>   virtio-net RSS" into patch "tun: Introduce virtio-net hash feature".
> - Dropped the RFC tag.
> - Link to v5: https://lore.kernel.org/r/20241008-rss-v5-0-f3cf68df005d@xxxxxxxxxx
>
> Changes in v5:
> - Fixed a compilation error with CONFIG_TUN_VNET_CROSS_LE.
> - Optimized the calculation of the hash value according to:
>   https://git.dpdk.org/dpdk/commit/?id=3fb1ea032bd6ff8317af5dac9af901f1f324cab4
> - Added patch "tun: Unify vnet implementation".
> - Dropped patch "tap: Pad virtio header with zero".
> - Added patch "selftest: tun: Test vnet ioctls without device".
> - Reworked selftests to skip for older kernels.
> - Documented the case when the underlying device is deleted and packets
>   have queue_mapping set by TC.
> - Reordered test harness arguments.
> - Added code to handle fragmented packets.
> - Link to v4: https://lore.kernel.org/r/20240924-rss-v4-0-84e932ec0e6c@xxxxxxxxxx
>
> Changes in v4:
> - Moved tun_vnet_hash_ext to if_tun.h.
> - Renamed virtio_net_toeplitz() to virtio_net_toeplitz_calc().
> - Replaced htons() with cpu_to_be16().
> - Changed virtio_net_hash_rss() to return void.
> - Reordered variable declarations in virtio_net_hash_rss().
> - Removed virtio_net_hdr_v1_hash_from_skb().
> - Updated messages of "tap: Pad virtio header with zero" and
>   "tun: Pad virtio header with zero".
> - Fixed vnet_hash allocation size.
> - Ensured to free vnet_hash when destructing tun_struct.
> - Link to v3: https://lore.kernel.org/r/20240915-rss-v3-0-c630015db082@xxxxxxxxxx
>
> Changes in v3:
> - Reverted back to add ioctl.
> - Split patch "tun: Introduce virtio-net hashing feature" into
>   "tun: Introduce virtio-net hash reporting feature" and
>   "tun: Introduce virtio-net RSS".
> - Changed to reuse hash values computed for automq instead of performing
>   RSS hashing when hash reporting is requested but RSS is not.
> - Extracted relevant data from struct tun_struct to keep it minimal.
> - Added kernel-doc.
> - Changed to allow calling TUNGETVNETHASHCAP before TUNSETIFF.
> - Initialized num_buffers with 1.
> - Added a test case for unclassified packets.
> - Fixed error handling in tests.
> - Changed tests to verify that the queue index will not overflow.
> - Rebased.
> - Link to v2: https://lore.kernel.org/r/20231015141644.260646-1-akihiko.odaki@xxxxxxxxxx
>
> ---
> Akihiko Odaki (6):
>       virtio_net: Add functions for hashing
>       net: flow_dissector: Export flow_keys_dissector_symmetric
>       tun: Introduce virtio-net hash feature
>       selftest: tun: Test vnet ioctls without device
>       selftest: tun: Add tests for virtio-net hashing
>       vhost/net: Support VIRTIO_NET_F_HASH_REPORT
>
>  Documentation/networking/tuntap.rst  |   7 +
>  drivers/net/Kconfig                  |   1 +
>  drivers/net/tap.c                    |  67 +++-
>  drivers/net/tun.c                    |  98 +++++-
>  drivers/net/tun_vnet.h               | 159 ++++++++-
>  drivers/vhost/net.c                  |  49 +--
>  include/linux/if_tap.h               |   2 +
>  include/linux/skbuff.h               |   3 +
>  include/linux/virtio_net.h           | 188 ++++++++++
>  include/net/flow_dissector.h         |   1 +
>  include/uapi/linux/if_tun.h          |  75 ++++
>  net/core/flow_dissector.c            |   3 +-
>  net/core/skbuff.c                    |   4 +
>  tools/testing/selftests/net/Makefile |   2 +-
>  tools/testing/selftests/net/tun.c    | 656 ++++++++++++++++++++++++++++++++++-
>  15 files changed, 1254 insertions(+), 61 deletions(-)
> ---
> base-commit: dd83757f6e686a2188997cb58b5975f744bb7786
> change-id: 20240403-rss-e737d89efa77
> prerequisite-change-id: 20241230-tun-66e10a49b0c7:v6
> prerequisite-patch-id: 871dc5f146fb6b0e3ec8612971a8e8190472c0fb
> prerequisite-patch-id: 2797ed249d32590321f088373d4055ff3f430a0e
> prerequisite-patch-id: ea3370c72d4904e2f0536ec76ba5d26784c0cede
> prerequisite-patch-id: 837e4cf5d6b451424f9b1639455e83a260c4440d
> prerequisite-patch-id: ea701076f57819e844f5a35efe5cbc5712d3080d
> prerequisite-patch-id: 701646fb43ad04cc64dd2bf13c150ccbe6f828ce
> prerequisite-patch-id: 53176dae0c003f5b6c114d43f936cf7140d31bb5
> prerequisite-change-id: 20250116-buffers-96e14bf023fc:v2
> prerequisite-patch-id: 25fd4f99d4236a05a5ef16ab79f3e85ee57e21cc
>
> Best regards,
> --
> Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
>