On Thu, Mar 02, 2023 at 10:57:12AM +0800, Jason Wang wrote: > On Wed, Mar 1, 2023 at 6:36 PM Michael S. Tsirkin <m...@redhat.com> wrote: > > > > On Wed, Mar 01, 2023 at 10:36:41AM +0800, Jason Wang wrote: > > > On Tue, Feb 28, 2023 at 7:05 PM Michael S. Tsirkin <m...@redhat.com> > > > wrote: > > > > > > > > On Tue, Feb 28, 2023 at 11:04:26AM +0800, Jason Wang wrote: > > > > > On Tue, Feb 28, 2023 at 1:49 AM Michael S. Tsirkin <m...@redhat.com> > > > > > wrote: > > > > > > > > > > > > On Mon, Feb 27, 2023 at 04:35:09PM +0800, Jason Wang wrote: > > > > > > > On Mon, Feb 27, 2023 at 3:39 PM Michael S. Tsirkin > > > > > > > <m...@redhat.com> wrote: > > > > > > > > > > > > > > > > On Mon, Feb 27, 2023 at 12:07:17PM +0800, Jason Wang wrote: > > > > > > > > > Btw, this kind of 1:1 hash features seems not scalable and > > > > > > > > > flexible. > > > > > > > > > It requires an endless extension on bits/fields. Modern NICs > > > > > > > > > allow the > > > > > > > > > user to customize the hash calculation, for virtio-net we can > > > > > > > > > allow to > > > > > > > > > use eBPF program to classify the packets. It seems to be more > > > > > > > > > flexible > > > > > > > > > and scalable and there's almost no maintain burden in the > > > > > > > > > spec (only > > > > > > > > > bytecode is required, no need any fancy features/interactions > > > > > > > > > like > > > > > > > > > maps), easy to be migrated etc. > > > > > > > > > > > > > > > > > > Prototype is also easy, tun/tap had an eBPF classifier for > > > > > > > > > years. > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > Yea BPF offload would be great to have. We have been discussing > > > > > > > > it for > > > > > > > > years though - security issues keep blocking it. *Maybe* it's > > > > > > > > finally > > > > > > > > going to be there but I'm not going to block this work waiting > > > > > > > > for BPF > > > > > > > > offload. And easily migrated is what BPF is not. > > > > > > > > > > > > > > Just to make sure we're at the same page. I meant to find a way to > > > > > > > allow the driver/user to fully customize what it wants to > > > > > > > hash/classify. Similar technologies which is based on private > > > > > > > solution > > > > > > > has been used by some vendors, which allow user to customize the > > > > > > > classifier[1] > > > > > > > > > > > > > > ePBF looks like a good open-source solution candidate for this > > > > > > > (there > > > > > > > could be others). But there could be many kinds of eBPF programs > > > > > > > that > > > > > > > could be offloaded. One famous one is XDP which requires many > > > > > > > features > > > > > > > other than the bytecode/VM like map access, tailcall. Starting > > > > > > > from > > > > > > > such a complicated type is hard. Instead, we can start from a > > > > > > > simple > > > > > > > type, that is the eBPF classifier. All it needs is to pass the > > > > > > > bytecode to the device, the device can choose to run it or > > > > > > > compile it > > > > > > > to what it can understand for classifying. We don't need maps, > > > > > > > tail > > > > > > > calls and other features. > > > > > > > > > > > > Until people start asking exactly for maps because they want > > > > > > state for their classifier? > > > > > > > > > > Yes, but let's compare the eBPF without maps with the static feature > > > > > proposed here. It is much more scalable and flexible. > > > > > > > > I looked for some examples of RSS using BPF and only found this: > > > > https://github.com/Netronome/bpf-samples/blob/master/programmable_rss/rss_user.c > > > > seems to use maps. > > > > > > Yes and this is also the way we emulate RSS with TUN/TAP via steering > > > eBPF support for TUN/TAP. The reason is that it needs to emulate not > > > only the hash but also the indirection. If we only replace the hash > > > function with the eBPF program but reuse the RSS indirection table, we > > > don't need maps. > > > > How? Add a special helper? > > We can let the eBPF program return the hash: > > [eBPF hasing] -> hash value -> [indirection table lookup] > > Note that if we don't consider future full eBPF offloading, we can > start with classical BPF. > > Thanks
So again this is a custom thing not a standard use of BPF. Normally value returned is pass/drop. > > > > > > > > > > > > > > > > And it makes sense - if you want > > > > > > e.g. load balancing you need stats which needs maps. > > > > > > > > > > Yes, but we know it's possible to have that (through the XDP offload). > > > > > > > > Not without a lot more work to make xdp offload happen. > > > > > > > > > > Yes, that's why a simple eBPF RSS hashing program looks much more easier. > > > > > > Thanks > > > > Notice that at this point this is no longer a generic BPF - you > > are using a special helper. For tunnels I would imagine two tables > > could easily turn out to be useful. Then what? Another table? > > If yes then I can't say I like where this is going ... > > > > > > > This is impossible with the approach proposed here. > > > > > > > > > > > > > > > > > > We don't need to worry about the security > > > > > > > because of its simplicity: the eBPF program is only in charge of > > > > > > > doing > > > > > > > classification, no other interactions with the driver and packet > > > > > > > modification is prohibited. The feature is limited only to the > > > > > > > VM/bytecode abstraction itself. > > > > > > > > > > > > > > What's more, it's a good first step to achieve full eBPF > > > > > > > offloading in > > > > > > > the future. > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > [1] > > > > > > > https://www.intel.com/content/www/us/en/architecture-and-technology/ethernet/dynamic-device-personalization-brief.html > > > > > > > > > > > > Dave seems to have nacked this approach, no? > > > > > > > > > > I may miss something but looking at kernel commit, there are few > > > > > patches to support that: > > > > > > > > > > E.g > > > > > > > > > > commit c7648810961682b9388be2dd041df06915647445 > > > > > Author: Tony Nguyen <anthony.l.ngu...@intel.com> > > > > > Date: Mon Sep 9 06:47:44 2019 -0700 > > > > > > > > > > ice: Implement Dynamic Device Personalization (DDP) download > > > > > > > > > > And it has been used by DPDK drivers. > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > MST > > > > > > > > > > > > > > > > > > > > --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org
