> Lorenzo Bianconi <lorenzo@xxxxxxxxxx> writes: > > >> > We could combine such a registration API with your header format, so > >> > that the registration just becomes a way of allocating one of the keys > >> > from 0-63 (and the registry just becomes a global copy of the header). > >> > This would basically amount to moving the "service config file" into the > >> > kernel, since that seems to be the only common denominator we can rely > >> > on between BPF applications (as all attempts to write a common daemon > >> > for BPF management have shown). > >> > >> That sounds reasonable. And I guess we'd have set() check the global > >> registry to enforce that the key has been registered beforehand? > >> > >> > > >> > -Toke > >> > >> Thanks for all the feedback! > > > > I like this 'fast' KV approach but I guess we should really evaluate its > > impact on performances (especially for xdp) since, based on the kfunc calls > > order in the ebpf program, we can have one or multiple memmove/memcpy for > > each packet, right? > > Yes, with Arthur's scheme, performance will be ordering dependent. Using > a global registry for offsets would sidestep this, but have the > synchronisation issues we discussed up-thread. So on balance, I think > the memmove() suggestion will probably lead to the least pain. > > For the HW metadata we could sidestep this by always having a fixed > struct for it (but using the same set/get() API with reserved keys). The > only drawback of doing that is that we statically reserve a bit of > space, but I'm not sure that is such a big issue in practice (at least > not until this becomes to popular that the space starts to be contended; > but surely 256 bytes ought to be enough for everybody, right? :)). I am fine with the proposed approach, but I think we need to verify what is the impact on performances (in the worst case??) > > > Moreover, I still think the metadata area in the xdp_frame/xdp_buff is not > > so suitable for nic hw metadata since: > > - it grows backward > > - it is probably in a different cacheline with respect to xdp_frame > > - nic hw metadata will not start at fixed and immutable address, but it depends > > on the running ebpf program > > > > What about having something like: > > - fixed hw nic metadata: just after xdp_frame struct (or if you want at the end > > of the metadata area :)). Here he can reuse the same KV approach if it is fast > > - user defined metadata: in the metadata area of the xdp_frame/xdp_buff > > AFAIU, none of this will live in the (current) XDP metadata area. It > will all live just after the xdp_frame struct (so sharing the space with > the metadata area in the sense that adding more metadata kv fields will > decrease the amount of space that is usable by the current XDP metadata > APIs). > > -Toke > ah, ok. I was thinking the proposed approach was to put them in the current metadata field. Regards, Lorenzo
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