Re: [dpdk-dev] L3fwd mode in testpmd

[Stanislaw Kardach <kda@semihalf.com>]

On Thu, Apr 29, 2021 at 08:31:03AM +0000, Ananyev, Konstantin wrote:
> Hi Stanislaw,
> 
> > 
> > On Wed, Apr 28, 2021 at 09:44:54PM +0000, Honnappa Nagarahalli wrote:
> > <snip>
> > > [Honnappa] Sorry, I do not understand this. I see that vector code is under compile time flag as below
> > >
> > > #if defined RTE_ARCH_X86 || defined __ARM_NEON
> > >                         l3fwd_em_send_packets(nb_rx, pkts_burst,
> > >                                                         portid, qconf);
> > > #else
> > >                        l3fwd_em_no_opt_send_packets(nb_rx, pkts_burst,
> > >                                                         portid, qconf);
> > > #endif
> > Take a look at the ifdef tree at the top of l3fwd_em.c, here:
> > http://git.dpdk.org/dpdk/tree/examples/l3fwd/l3fwd_em.c#n218
> > 
> > #if defined(__SSE2__)
> > ...
> > #else
> > #error No vector engine (SSE, NEON, ALTIVEC) available, check your toolchain
> > #endif
> > 
> 
> I think it is just a flaw and needs to be fixed.
> Patch would help here 😊
> Konstantin

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.
:)

-- 
Best Regards,
Stanislaw Kardach