On 2025/03/12 11:59, Jason Wang wrote:
On Tue, Mar 11, 2025 at 2:17 PM Akihiko Odaki akihiko.odaki@daynix.com wrote:
On 2025/03/11 9:38, Jason Wang wrote:
On Mon, Mar 10, 2025 at 3:45 PM Akihiko Odaki akihiko.odaki@daynix.com wrote:
On 2025/03/10 12:55, Jason Wang wrote:
On Fri, Mar 7, 2025 at 7:01 PM Akihiko Odaki akihiko.odaki@daynix.com 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@daynix.com Tested-by: Lei Yang leiyang@redhat.com
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(-)[...]
Let's has a consistent name for this and the uapi to be consistent with TUNSETIFF/TUNGETIFF. Probably TUNSETVNETHASH and tun_vnet_ioctl_gethash().
They have different semantics so they should have different names. TUNGETIFF reports the value currently set while TUNGETVNETHASHCAP reports the value that can be set later.
I'm not sure I will get here. I meant a symmetric name
TUNSETVNETHASH and TUNVETVNETHASH.
TUNGETVNETHASHCAP does not correspond to TUNGETIFF. The correspondence of ioctl names is as follows: TUNGETFEATURES - TUNGETVNETHASHCAP
TUNGETFEATURES returns the value set from TUNSETIFF. This differs from TUNGETVNETHASHCAP semantic which just return the capabilities.
+static inline long tun_vnet_ioctl_gethashcap(void __user *argp) +{
static const struct tun_vnet_hash cap = {.flags = TUN_VNET_HASH_REPORT | TUN_VNET_HASH_RSS,.types = VIRTIO_NET_SUPPORTED_HASH_TYPES};return copy_to_user(argp, &cap, sizeof(cap)) ? -EFAULT : 0;+}
TUNGETFEATURES doesn't' help too much for non-persist TAP as userspace knows what value it set before.
TUNSETIFF - TUNSETVNETHASH TUNGETIFF - no corresponding ioctl for the virtio-net hash features
And this sounds odd and a hint for a incomplete uAPI as userspace needs to know knowing what can set before doing TUNSETVNETHASH.
You are confused with TUNGETFEATURES and TUNGETIFF. Below is the code that implements TUNGETFEATURES: if (cmd == TUNGETFEATURES) { /* Currently this just means: "what IFF flags are valid?". * This is needed because we never checked for invalid flags on * TUNSETIFF. */ return put_user(IFF_TUN | IFF_TAP | IFF_NO_CARRIER | TUN_FEATURES, (unsigned int __user*)argp); } else if (cmd == TUNSETQUEUE) {
Regards, Akihiko Odaki
Regards, Akihiko Odaki
Thanks