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Message-ID: <20250716045513-mutt-send-email-mst@kernel.org> Date: Wed, 16 Jul 2025 04:55:30 -0400 From: "Michael S. Tsirkin" <mst@...hat.com> To: Akihiko Odaki <akihiko.odaki@...nix.com> Cc: Jonathan Corbet <corbet@....net>, Willem de Bruijn <willemdebruijn.kernel@...il.com>, Jason Wang <jasowang@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, Yuri Benditovich <yuri.benditovich@...nix.com>, Andrew Melnychenko <andrew@...nix.com>, Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com, Lei Yang <leiyang@...hat.com>, Simon Horman <horms@...nel.org> Subject: Re: [PATCH net-next v12 00/10] tun: Introduce virtio-net hashing feature 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@...nix.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@...nix.com>
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