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Subject: RE: [PATCH v2 2/2] lpm: add a scalar version of lookupx4 function
Date: Mon, 30 May 2022 10:00:34 +0200
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D870C0@smartserver.smartshare.dk>
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Thread-Topic: [PATCH v2 2/2] lpm: add a scalar version of lookupx4 function
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References: <20220510115824.457885-1-kda@semihalf.com>
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Bruce Richardson" <bruce.richardson@intel.com>,
 "Stephen Hemminger" <stephen@networkplumber.org>
Cc: "Stanislaw Kardach" <kda@semihalf.com>,
 "Vladimir Medvedkin" <vladimir.medvedkin@intel.com>,
 "Michal Mazurek" <maz@semihalf.com>, <dev@dpdk.org>,
 "Frank Zhao" <Frank.Zhao@starfivetech.com>,
 "Sam Grove" <sam.grove@sifive.com>, <mw@semihalf.com>,
 <upstream@semihalf.com>
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> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Monday, 30 May 2022 09.52
>=20
> On Fri, May 27, 2022 at 01:15:20PM -0700, Stephen Hemminger wrote:
> > On Fri, 27 May 2022 20:18:22 +0200
> > Stanislaw Kardach <kda@semihalf.com> wrote:
> >
> > > +static inline void
> > > +rte_lpm_lookupx4(const struct rte_lpm *lpm, xmm_t ip, uint32_t
> hop[4],
> > > +		uint32_t defv)
> > > +{
> > > +	uint32_t nh;
> > > +	int i, ret;
> > > +
> > > +	for (i =3D 0; i < 4; i++) {
> > > +		ret =3D rte_lpm_lookup(lpm, ((rte_xmm_t)ip).u32[i], &nh);
> > > +		hop[i] =3D (ret =3D=3D 0) ? nh : defv;
> > > +	}
> > > +}
> >
> > For performance, manually unroll the loop.
>=20
> Given a constant 4x iterations, will compilers not unroll this
> automatically. I think the loop is a little clearer if it can be kept
>=20
> /Bruce

If in doubt, add this and look at the assembler output:

#define REVIEW_INLINE_FUNCTIONS 1

#if REVIEW_INLINE_FUNCTIONS /* For compiler output review purposes only. =
*/
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wmissing-prototypes"
void review_rte_lpm_lookupx4(const struct rte_lpm *lpm, xmm_t ip, =
uint32_t hop[4], uint32_t defv)
{
	rte_lpm_lookupx4(lpm, ip, hop, defv);
}
#pragma GCC diagnostic pop
#endif /* REVIEW_INLINE_FUNCTIONS */