netdev - Re: [PATCH RFC PoC 0/3] nftables meets bpf

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Date:   Wed, 21 Feb 2018 16:30:07 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jakub Kicinski <kubakici@...pl>,
        Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, laforge@...filter.org, fw@...len.de,
        alexei.starovoitov@...il.com
Subject: Re: [PATCH RFC PoC 0/3] nftables meets bpf

On 02/21/2018 03:46 PM, Jakub Kicinski wrote:
> On Tue, 20 Feb 2018 11:58:22 +0100, Pablo Neira Ayuso wrote:
>> We also have a large range of TCAM based hardware offload outthere
>> that will _not_ work with your BPF HW offload infrastructure. What
>> this bpf infrastructure pushes into the kernel is just a blob
>> expressing things in a very low-level instruction-set: trying to find
>> a mapping of that to typical HW intermediate representations in the
>> TCAM based HW offload world will be simply crazy.
> 
> I'm not sure where the TCAM talk is coming from.  Think much smaller -
> cellular modems/phone SoCs, 32bit ARM/MIPS router box CPUs.  The
> information the verifier is gathering will be crucial for optimizing
> those.  Please don't discount the value of being able to use
> heterogeneous processing units by the networking stack.
> 

The only use case that we have a good answer for is when there is no HW
offload capability available, because there, we know that eBPF is our
best possible solution for a software fast path, in large part because
of all the efforts that went into making it both safe and fast.

When there is offloading HW available, there does not appear to be a
perfect answer to this problem of, given a standard Linux utility that
can express any sort of match + action, be it ethtool::rxnfc,
tc/cls_{u32,flower}, nftables, how do I transform that into what makes
most sense to my HW? You could:

- have hardware that understands BPF bytecode directly, great, then you
don't have to do anything, just pass it up the driver baby, oh wait,
it's not that simple, the NFP driver is not small

- transform BPF back into something that your hardware understand, does
that belong in the kernel? Maybe, maybe not

- use a completely different intermediate representation like P4,
brainfuck, I don't know

Maybe first things first, we have at least 3 different programming
interfaces, if not more: ethtool::rxnfc, tc/cls_{u32,flower}, nftables
that are all capable of programming TCAMs and hardware capable of match
+ action, how about we start with having some sort of common library
code that:

- validates input parameters against HW capabilities
- does the adequate transformation from any of these interfaces into a
generic set of input parameters
- define what the appropriate behavior is when programming through all
of these 3 interfaces that ultimately access the same shared piece of
HW, and therefore need to manage resources allocation?

</rant>
-- 
Florian