[dpdk-dev] [RFC PATCH] lpm: add sve support for lookup on Arm platform

[Medvedkin, Vladimir]

Hi Ruifeng,

Thanks for the patch, see comments below

On 18/12/2020 10:12, Ruifeng Wang wrote:
> Added new path to do lpm4 lookup by using scalable vector extension.
> The SVE path will be selected if compiler has flag SVE set.
> 
> Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
> ---
>   lib/librte_eal/arm/include/rte_vect.h |  3 +
>   lib/librte_lpm/meson.build            |  2 +-
>   lib/librte_lpm/rte_lpm.h              |  4 ++
>   lib/librte_lpm/rte_lpm_sve.h          | 83 +++++++++++++++++++++++++++
>   4 files changed, 91 insertions(+), 1 deletion(-)
>   create mode 100644 lib/librte_lpm/rte_lpm_sve.h
> 
> diff --git a/lib/librte_eal/arm/include/rte_vect.h b/lib/librte_eal/arm/include/rte_vect.h
> index a739e6e66..093e9122a 100644
> --- a/lib/librte_eal/arm/include/rte_vect.h
> +++ b/lib/librte_eal/arm/include/rte_vect.h
> @@ -9,6 +9,9 @@
>   #include "generic/rte_vect.h"
>   #include "rte_debug.h"
>   #include "arm_neon.h"
> +#ifdef __ARM_FEATURE_SVE
> +#include <arm_sve.h>
> +#endif
>   
>   #ifdef __cplusplus
>   extern "C" {
> diff --git a/lib/librte_lpm/meson.build b/lib/librte_lpm/meson.build
> index 6cfc083c5..f93c86640 100644
> --- a/lib/librte_lpm/meson.build
> +++ b/lib/librte_lpm/meson.build
> @@ -5,6 +5,6 @@ sources = files('rte_lpm.c', 'rte_lpm6.c')
>   headers = files('rte_lpm.h', 'rte_lpm6.h')
>   # since header files have different names, we can install all vector headers
>   # without worrying about which architecture we actually need
> -headers += files('rte_lpm_altivec.h', 'rte_lpm_neon.h', 'rte_lpm_sse.h')
> +headers += files('rte_lpm_altivec.h', 'rte_lpm_neon.h', 'rte_lpm_sse.h', 'rte_lpm_sve.h')
>   deps += ['hash']
>   deps += ['rcu']
> 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..86576ec52
> --- /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
> +__rte_lpm_lookup_vec(const struct rte_lpm *lpm, const uint32_t *ips,
> +		uint32_t *__rte_restrict next_hops, const uint32_t n)
> +{
> +	uint32_t i = 0;
> +	svuint32_t v_ip, v_idx, v_tbl24, v_tbl8, v_hop;
> +	svuint32_t v_mask_xv, v_mask_v, v_mask_hop;
> +	svbool_t pg = svwhilelt_b32(i, n);
> +	svbool_t pv;
> +
> +	do {
> +		v_ip = svld1(pg, &ips[i]);
> +		/* Get indices for tbl24[] */
> +		v_idx = svlsr_x(pg, v_ip, 8);
> +		/* Extract values from tbl24[] */
> +		v_tbl24 = svld1_gather_index(pg, (const uint32_t *)lpm->tbl24,
> +						v_idx);
> +
> +		/* Create mask with valid set */
> +		v_mask_v = svdup_u32_z(pg, RTE_LPM_LOOKUP_SUCCESS);
> +		/* Create mask with valid and valid_group set */
> +		v_mask_xv = svdup_u32_z(pg, RTE_LPM_VALID_EXT_ENTRY_BITMASK);
> +		/* Create predicate for tbl24 entries: (valid && !valid_group) */
> +		pv = svcmpeq(pg, svand_z(pg, v_tbl24, v_mask_xv), v_mask_v);
> +		/* Create mask for next_hop in table entry */
> +		v_mask_hop = svdup_u32_z(pg, 0x00ffffff);
> +		/* Extract next_hop and write back */
> +		v_hop = svand_x(pv, v_tbl24, v_mask_hop);
> +		svst1(pv, &next_hops[i], v_hop);
> +
> +		/* Update predicate for tbl24 entries: (valid && valid_group) */
> +		pv = svcmpeq(pg, svand_z(pg, v_tbl24, v_mask_xv), v_mask_xv);
> +		/* Compute tbl8 index */
> +		v_idx = svand_x(pv, v_tbl24, svdup_u32_z(pv, 0xff));

Loos like here should be
v_idx = svand_x(pv, v_tbl24, svdup_u32_z(pv, 0xffffff));
because we are using 24 bits to keep tbl8 group.


> +		v_idx = svmul_x(pv, v_idx, RTE_LPM_TBL8_GROUP_NUM_ENTRIES);
> +		v_idx = svadd_x(pv, svand_x(pv, v_ip, svdup_u32_z(pv, 0xff)),
> +				v_idx);
> +		/* Extract values from tbl8[] */
> +		v_tbl8 = svld1_gather_index(pv, (const uint32_t *)lpm->tbl8,
> +						v_idx);
> +		/* Update predicate for tbl8 entries: (valid) */
> +		pv = svcmpeq(pv, svand_z(pv, v_tbl8, v_mask_v), v_mask_v);
> +		/* Extract next_hop and write back */
> +		v_hop = svand_x(pv, v_tbl8, v_mask_hop);
> +		svst1(pv, &next_hops[i], v_hop);

I'm not an expert, but probably it would be better to merge two stores 
(svst1) into a single one?

> +
> +		i += svlen(v_ip);
> +		pg = svwhilelt_b32(i, n);

Isn't it better to move the predicate calculation to the beginning of 
the loop and just do {} while (i < n)?

> +	} while (svptest_any(svptrue_b32(), pg));
> +}
> +
> +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);
> +}
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_LPM_SVE_H_ */
> 

-- 
Regards,
Vladimir