Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > Tow main drivers on my side: > > - there are use cases/deployments that do not use them. > > - moving them around was doable in term of required changes. > > > > There are no "slow-path" implications on my side. For example, vlan_* > > fields are very critical performance wise, if the traffic is tagged. > > But surely there are busy servers not using tagget traffic which will > > enjoy the reduced cachelines footprint, and this changeset will not > > impact negatively the first case. > > > > WRT to the vlan example, secmark and nfct require an extra conditional > > to fetch the data. My understanding is that such additional conditional > > is not measurable performance-wise when benchmarking the security > > modules (or conntrack) because they have to do much more intersting > > things after fetching a few bytes from an already hot cacheline. > > > > Not sure if the above somehow clarify my statements. > > > > As for expanding secmark to 64 bits, I guess that could be an > > interesting follow-up discussion :) > > The intersection between netdev and the LSM has a long and somewhat > tortured past with each party making sacrifices along the way to get > where we are at today. It is far from perfect, at least from a LSM > perspective, but it is what we've got and since performance is usually > used as a club to beat back any changes proposed by the LSM side, I > would like to object to these changes that negatively impact the LSM > performance without some concession in return. It has been a while > since Casey and I have spoken about this, but I think the prefered > option would be to exchange the current __u32 "sk_buff.secmark" field > with a void* "sk_buff.security" field, like so many other kernel level > objects. Previous objections have eventually boiled down to the > additional space in the sk_buff for the extra bits (there is some > additional editorializing that could be done here, but I'll refrain), > but based on the comments thus far in this thread it sounds like > perhaps we can now make a deal here: move the LSM field down to a > "colder" cacheline in exchange for converting the LSM field to a > proper pointer. > > Thoughts? Is there a summary disucssion somewhere wrt. what exactly LSMs need? There is the skb extension infra, does that work for you?
