On Mon, Jun 25, 2018 at 11:43 PM, Jiri Pirko <j...@resnulli.us> wrote: > Tue, Jun 26, 2018 at 06:58:50AM CEST, jakub.kicin...@netronome.com wrote: >>On Mon, 25 Jun 2018 23:01:39 +0200, Jiri Pirko wrote: >>> From: Jiri Pirko <j...@mellanox.com> >>> >>> For the TC clsact offload these days, some of HW drivers need >>> to hold a magic ball. The reason is, with the first inserted rule inside >>> HW they need to guess what fields will be used for the matching. If >>> later on this guess proves to be wrong and user adds a filter with a >>> different field to match, there's a problem. Mlxsw resolves it now with >>> couple of patterns. Those try to cover as many match fields as possible. >>> This aproach is far from optimal, both performance-wise and scale-wise. >>> Also, there is a combination of filters that in certain order won't >>> succeed. >>> >>> Most of the time, when user inserts filters in chain, he knows right away >>> how the filters are going to look like - what type and option will they >>> have. For example, he knows that he will only insert filters of type >>> flower matching destination IP address. He can specify a template that >>> would cover all the filters in the chain. >> >>Perhaps it's lack of sleep, but this paragraph threw me a little off >>the track. IIUC the goal of this set is to provide a way to inform the >>HW about expected matches before any rule is programmed into the HW. >>Not before any rule is added to a particular chain. One can just use >>the first rule in the chain to make a guess about the chain, but thanks >>to this set user can configure *all* chains before any rules are added. > > The template is per-chain. User can use template for chain x and > not-use it for chain y. Up to him.
Makes sense. I can't help but wonder if it'd be better to associate the constraints/rules with chains instead of creating a new "template" object. It seems more natural to create a chain with specific constraints in place than add and delete template of which there can be at most one to a chain... Perhaps that's more about the user space tc command line. Anyway, not a strong objection, just a thought. >>And that's needed because once any rule is added the tcam config can no >>longer be easily modified? > > Yes.
