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

[David Marchand <david.marchand@redhat.com>]

On Wed, Jan 27, 2021 at 10:03 PM Honnappa Nagarahalli
<Honnappa.Nagarahalli@arm.com> wrote:
>
> <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?

It happens that drivers/libraries in DPDK offer some interface for
other parts of the DPDK to use.
But we might want them to keep them hidden to final applications,
because this is purely internal and/or we don't want to guarantee
compatibility in later versions.
For such cases, a function can be marked __rte_internal.


This tag has two impacts:
- a marked symbol is versionned as INTERNAL when exported (so this
does not apply to inlines),
- if an application tries to use a marked API, an error is triggered
at build time to prevent use of such API,


-- 
David Marchand