Re: [dpdk-dev] L3fwd mode in testpmd

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> 
> On Thu, Apr 29, 2021 at 11:47:30AM +0000, Ananyev, Konstantin wrote:
> <snip>
> > >
> > > It looks as if implementing em_mask_key() is enough to get l3fwd
> > > working. However to me this ifdef seems tricky. How should a scalar
> > > implementation handle the xmm_t type? rte_xmm_t looks like an API
> > > type/union, but both are not mentioned in documentation and are in
> > > platform dependent rte_vect.h only.
> > > So either I add another case for RISC-V or (what seems more proper) add
> > > an else clause implementation. However then should I change this function
> > > to take rte_xmm_t? If not is casting xmm_t to i.e. int32_t[] always
> > > valid? Even if I change to rte_xmm_t, it's not a stable API type, is it?
> > > So what guarantee do I have that it maps to int32_t bit-wise on every
> > > platform?
> > >
> > > I think the semantic requirements of xmm_t typedef are a bit undefined as
> > > well as the vector handling across the architectures (being something
> > > rather arch specific). I don't have a clear idea on how to solve this
> > > yet and I would not like to hijack this discussion with vector stuff.
> > >
> > > Though I may be missing some obvious solution here. Any idea is welcome.
> > > :)
> >
> > I think it should be possible to replace xmm_t with rte_xmm_t in ipv(4|6)_5tuple_host
> > and make em_mask_key to take 'rte_xmm_t *' as a parameter/return value instead of xmm_t.
> > With that in place scalar version seems straightforward.
> > Of course perf regression test would be needed after such changes,
> > but I think with '-O3' it should be no difference.
> >
> I did that and it works in practice. I'm more asking about the lack of
> definition in rte_xmm_t semantics. Because once it's in an example,
> people may start assuming it's OK to use it this way.
> If it is OK, then I'll just post a patch, otherwise we need a separate
> discussion.

From my perspective: rte_xmm_t is a union used to simplify SIMD-related
code development. It contains HW specific field (xmm_t) and common ones.
It is not used in public DPDK API, but it is used quite extensively inside various libs.
As a public structure - so it can be used by examples and user code
(as long as it is defined for the given architecture).
So I suppose it is up to you guys to decide do you want to define it for your architecture or not.
If not, but you would still like to run l3fwd, then probably l3fwd_em.c needs to be split
Into l3fwd_em_scalar.c and l3fwd_em_vect.c.  

Konstantin