Re: [PATCH net-next v12 00/10] tun: Introduce virtio-net hashing feature

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, May 30, 2025 at 01:50:04PM +0900, Akihiko Odaki wrote:
> NOTE: I'm leaving Daynix Computing Ltd., for which I worked on this
> patch series, by the end of this month.
> 
> While net-next is closed, this is the last chance for me to send another
> version so let me send the local changes now.
> 
> Please contact Yuri Benditovich, who is CCed on this email, for anything
> about this series.
> 
> 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/20250530-hash-v5-0-343d7d7a8200@daynix.com/
> 
> This work was presented at LPC 2024:
> https://lpc.events/event/18/contributions/1963/


It's been a while, do you intend to post v13?

> V1 -> V2:
>   Changed to introduce a new BPF program type.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> Changes in v12:
> - Updated tools/testing/selftests/net/config.
> - Split TUNSETVNETHASH.
> - Link to v11: https://lore.kernel.org/r/20250317-rss-v11-0-4cacca92f31f@daynix.com
> 
> Changes in v11:
> - Added the missing code to free vnet_hash in patch
>   "tap: Introduce virtio-net hash feature".
> - Link to v10: https://lore.kernel.org/r/20250313-rss-v10-0-3185d73a9af0@daynix.com
> 
> Changes in v10:
> - Split common code and TUN/TAP-specific code into separate patches.
> - Reverted a spurious style change in patch "tun: Introduce virtio-net
>   hash feature".
> - Added a comment explaining disable_ipv6 in tests.
> - Used AF_PACKET for patch "selftest: tun: Add tests for
>   virtio-net hashing". I also added the usage of FIXTURE_VARIANT() as
>   the testing function now needs access to more variant-specific
>   variables.
> - Corrected the message of patch "selftest: tun: Add tests for
>   virtio-net hashing"; it mentioned validation of configuration but
>   it is not scope of this patch.
> - Expanded the description of patch "selftest: tun: Add tests for
>   virtio-net hashing".
> - Added patch "tun: Allow steering eBPF program to fall back".
> - Changed to handle TUNGETVNETHASHCAP before taking the rtnl lock.
> - Removed redundant tests for tun_vnet_ioctl().
> - Added patch "selftest: tap: Add tests for virtio-net ioctls".
> - Added a design explanation of ioctls for extensibility and migration.
> - Removed a few branches in patch
>   "vhost/net: Support VIRTIO_NET_F_HASH_REPORT".
> - Link to v9: https://lore.kernel.org/r/20250307-rss-v9-0-df76624025eb@daynix.com
> 
> Changes in v9:
> - Added a missing return statement in patch
>   "tun: Introduce virtio-net hash feature".
> - Link to v8: https://lore.kernel.org/r/20250306-rss-v8-0-7ab4f56ff423@daynix.com
> 
> 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@daynix.com
> 
> 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@daynix.com
> 
> 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@daynix.com
> 
> 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@daynix.com
> 
> 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@daynix.com
> 
> 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@daynix.com
> 
> ---
> Akihiko Odaki (10):
>       virtio_net: Add functions for hashing
>       net: flow_dissector: Export flow_keys_dissector_symmetric
>       tun: Allow steering eBPF program to fall back
>       tun: Add common virtio-net hash feature code
>       tun: Introduce virtio-net hash feature
>       tap: Introduce virtio-net hash feature
>       selftest: tun: Test vnet ioctls without device
>       selftest: tun: Add tests for virtio-net hashing
>       selftest: tap: Add tests for virtio-net ioctls
>       vhost/net: Support VIRTIO_NET_F_HASH_REPORT
> 
>  Documentation/networking/tuntap.rst  |   7 +
>  drivers/net/Kconfig                  |   1 +
>  drivers/net/ipvlan/ipvtap.c          |   2 +-
>  drivers/net/macvtap.c                |   2 +-
>  drivers/net/tap.c                    |  80 +++++-
>  drivers/net/tun.c                    |  92 +++++--
>  drivers/net/tun_vnet.h               | 165 +++++++++++-
>  drivers/vhost/net.c                  |  68 ++---
>  include/linux/if_tap.h               |   4 +-
>  include/linux/skbuff.h               |   3 +
>  include/linux/virtio_net.h           | 188 ++++++++++++++
>  include/net/flow_dissector.h         |   1 +
>  include/uapi/linux/if_tun.h          |  80 ++++++
>  net/core/flow_dissector.c            |   3 +-
>  net/core/skbuff.c                    |   4 +
>  tools/testing/selftests/net/Makefile |   2 +-
>  tools/testing/selftests/net/config   |   1 +
>  tools/testing/selftests/net/tap.c    | 131 +++++++++-
>  tools/testing/selftests/net/tun.c    | 485 ++++++++++++++++++++++++++++++++++-
>  19 files changed, 1234 insertions(+), 85 deletions(-)
> ---
> base-commit: 5cb8274d66c611b7889565c418a8158517810f9b
> change-id: 20240403-rss-e737d89efa77
> 
> Best regards,
> -- 
> Akihiko Odaki <akihiko.odaki@daynix.com>