Re: [RFC 06/12] nfp: add hardware cls_bpf offload

[Jakub Kicinski <jakub.kicinski@netronome.com>]

On Wed, 1 Jun 2016 13:52:01 -0700, Alexei Starovoitov wrote:
> On Wed, Jun 01, 2016 at 10:20:54PM +0200, Daniel Borkmann wrote:
> > On 06/01/2016 06:50 PM, Jakub Kicinski wrote:  
> > >Add hardware cls_bpf offload on our smart NICs.  Detect if
> > >capable firmware is loaded and use it to load the code JITed
> > >with just added translator onto programmable engines.
> > >
> > >Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> > >Reviewed-by: Dinan Gunawardena <dgunawardena@netronome.com>
> > >Reviewed-by: Simon Horman <simon.horman@netronome.com>  
> > [...]  
> > >+static int
> > >+nfp_net_bpf_offload_prepare(struct nfp_net *nn,
> > >+			    struct tc_cls_bpf_offload *cls_bpf,
> > >+			    struct nfp_bpf_result *res,
> > >+			    void **code, dma_addr_t *dma_addr, u16 max_instr)
> > >+{
> > >+	unsigned int code_sz = max_instr * sizeof(u64);
> > >+	u16 start_off, tgt_out, tgt_abort;
> > >+	const struct tc_action *a;
> > >+	int err;
> > >+
> > >+	if (tc_no_actions(cls_bpf->exts))
> > >+		return -EINVAL;
> > >+
> > >+	tc_for_each_action(a, cls_bpf->exts) {
> > >+		if (!is_tcf_gact_shot(a))
> > >+			return -EINVAL;
> > >+	}
> > >+
> > >+	if (cls_bpf->exts_integrated)
> > >+		return -EINVAL;  
> > 
> > So cls_bpf has two working modes as mentioned: da (direct-action) and non-da.
> > Direct-action is I would say the most typical way to run cls_bpf as it allows
> > you to more naturally and efficiently code programs in the sense that classification
> > and action is already combined in a single program, so there's no additional
> > overhead of a linear action chain required, and a single program can already
> > have multiple action code outcomes (TC_ACT_OK, TC_ACT_SHOT, ...), so that it is
> > usually enough to run a single cls_bpf instance, for example, on sch_clsact
> > ingress or egress parent, nothing more than that to get the job done. I think
> > the cls_bpf->exts_integrated test could probably come first and if it's false,
> > we'd need to walk the actions?  
> 
> I think it makes sense to offload da mode only. Doing tc_for_each_action
> walk like above is ok, but the number of bpf programs with only separate
> gact is diminishingly small and we don't recommend to use it anymore.
> That's the stuff we used when da wasn't available.
 
Let me make sure I understand - to get da offloaded I would have to
check that all return values are either OK or SHOT?  That was my
understanding but since it would make the initial submission more
complex I decided against it...