Re: [dpdk-dev] [PATCH v3 1/5] lpm: add sve support for lookup on Arm platform

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> On Tue, Jan 12, 2021 at 3:57 AM Ruifeng Wang <ruifeng.wang@arm.com>
> wrote:
> > diff --git a/lib/librte_lpm/rte_lpm.h b/lib/librte_lpm/rte_lpm.h index
> > 1afe55cdc..28b57683b 100644
> > --- a/lib/librte_lpm/rte_lpm.h
> > +++ b/lib/librte_lpm/rte_lpm.h
> > @@ -402,7 +402,11 @@ rte_lpm_lookupx4(const struct rte_lpm *lpm,
> xmm_t ip, uint32_t hop[4],
> >         uint32_t defv);
> >
> >  #if defined(RTE_ARCH_ARM)
> > +#ifdef __ARM_FEATURE_SVE
> > +#include "rte_lpm_sve.h"
> > +#else
> >  #include "rte_lpm_neon.h"
> > +#endif
> >  #elif defined(RTE_ARCH_PPC_64)
> >  #include "rte_lpm_altivec.h"
> >  #else
> > diff --git a/lib/librte_lpm/rte_lpm_sve.h
> > b/lib/librte_lpm/rte_lpm_sve.h new file mode 100644 index
> > 000000000..2e319373e
> > --- /dev/null
> > +++ b/lib/librte_lpm/rte_lpm_sve.h
> > @@ -0,0 +1,83 @@
> > +/* SPDX-License-Identifier: BSD-3-Clause
> > + * Copyright(c) 2020 Arm Limited
> > + */
> > +
> > +#ifndef _RTE_LPM_SVE_H_
> > +#define _RTE_LPM_SVE_H_
> > +
> > +#include <rte_vect.h>
> > +
> > +#ifdef __cplusplus
> > +extern "C" {
> > +#endif
> > +
> > +__rte_internal
> > +static void
> 
> I was looking into use of the __rte_internal tag in the tree.
> 
> This helper is called from a inlined API used by applications, so out of the
> DPDK build.
> It looks like the compiler is not complaining when compiling examples (I
> hacked my env to cross compile with gcc 10 + SVE enabled) but this seems
> incorrect to me.
> 
> Is there really a need for this helper?
> It is only used below afaics.
I do not think it is required.

At the same time the commit log when '__rte_internal' was introduced is confusing.
It says "Introduce the __rte_internal tag to mark internal ABI function which is used only by the drivers or other libraries". Why would an internal function have an ABI?

> 
> 
> > +__rte_lpm_lookup_vec(const struct rte_lpm *lpm, const uint32_t *ips,
> > +               uint32_t *__rte_restrict next_hops, const uint32_t n)
> > +{
> 
> [snip]
> 
> 
> > +}
> > +
> > +static inline void
> > +rte_lpm_lookupx4(const struct rte_lpm *lpm, xmm_t ip, uint32_t hop[4],
> > +               uint32_t defv)
> > +{
> > +       uint32_t i, ips[4];
> > +
> > +       vst1q_s32((int32_t *)ips, ip);
> > +       for (i = 0; i < 4; i++)
> > +               hop[i] = defv;
> > +
> > +       __rte_lpm_lookup_vec(lpm, ips, hop, 4); }
> 
> 
> --
> David Marchand