On Mon, Mar 10, 2025 at 11:55 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > On Fri, Mar 7, 2025 at 7:01 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote: > > > > Hash reporting > > ============== > > > > Allow the guest to reuse the hash value to make receive steering > > consistent between the host and guest, and to save hash computation. > > > > RSS > > === > > > > RSS is a receive steering algorithm that can be negotiated to use with > > virtio_net. 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 steering program. > > > > Introduce the code to perform RSS 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 I didn't > > opt for it because extending the current mechanism of eBPF steering > > program as is because it relies on legacy context rewriting, and > > introducing kfunc-based eBPF will result in non-UAPI dependency while > > the other relevant virtualization APIs such as KVM and vhost_net are > > UAPIs. > > > > Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> > > Tested-by: Lei Yang <leiyang@xxxxxxxxxx> > > --- > > Documentation/networking/tuntap.rst | 7 ++ > > drivers/net/Kconfig | 1 + > > drivers/net/tap.c | 68 ++++++++++++++- > > drivers/net/tun.c | 98 +++++++++++++++++----- > > drivers/net/tun_vnet.h | 159 ++++++++++++++++++++++++++++++++++-- > > include/linux/if_tap.h | 2 + > > include/linux/skbuff.h | 3 + > > include/uapi/linux/if_tun.h | 75 +++++++++++++++++ > > net/core/skbuff.c | 4 + > > 9 files changed, 386 insertions(+), 31 deletions(-) [...] > > + * > > + * The %TUN_VNET_HASH_REPORT flag set with this ioctl will be effective only > > + * after calling the %TUNSETVNETHDRSZ ioctl with a number greater than or equal > > + * to the size of &struct virtio_net_hdr_v1_hash. > > So you had a dependency check already for vnet hdr len. I'd still > suggest to split this into rss and hash as they are separated > features. Then we can use separate data structure for them instead of > a container struct. > Besides this, I think we still need to add new bits to TUNGETIFF to let userspace know about the new ability. Thanks
