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

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

On Thu, 2 Jun 2016 08:57:48 +0200, Jiri Pirko wrote:
> Wed, Jun 01, 2016 at 11:36:48PM CEST, john.fastabend@gmail.com wrote:
> >On 16-06-01 01:52 PM, 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.
> >>   
> >
> >+1 I've been using da mode only as well.  
> 
> I also think we should support offload for da mode only for cls_bpf

First of all thanks everyone for the reviews and suggestions!

I will definitely do da in the next revision, but I'm not sure we
should do only da.  As far as I can tell there are no statistics when
da mode is used.