[PATCH v6 4/4] hash: add SVE support for bulk key lookup

[fengchengwen]

Hi Yoan,

On 2024/3/12 7:21, Yoan Picchi wrote:
> - Implemented SVE code for comparing signatures in bulk lookup.
> - Added Defines in code for SVE code support.
> - Optimise NEON code

This commit does not include this part. Pls only describe the content in this commit.

> - New SVE code is ~5% slower than optimized NEON for N2 processor.
> 
> Signed-off-by: Yoan Picchi <yoan.picchi at arm.com>
> Signed-off-by: Harjot Singh <harjot.singh at arm.com>
> Reviewed-by: Nathan Brown <nathan.brown at arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
> ---
>  lib/hash/arch/arm/compare_signatures.h | 58 ++++++++++++++++++++++++++
>  lib/hash/rte_cuckoo_hash.c             |  2 +
>  2 files changed, 60 insertions(+)
> 
> diff --git a/lib/hash/arch/arm/compare_signatures.h b/lib/hash/arch/arm/compare_signatures.h
> index b5a457f936..8a0627e119 100644
> --- a/lib/hash/arch/arm/compare_signatures.h
> +++ b/lib/hash/arch/arm/compare_signatures.h
> @@ -47,6 +47,64 @@ compare_signatures_dense(uint16_t *hitmask_buffer,
>  		*hitmask_buffer = vaddvq_u16(hit2);
>  		}
>  		break;
> +#endif
> +#if defined(RTE_HAS_SVE_ACLE)
> +	case RTE_HASH_COMPARE_SVE: {

...

>  #endif
>  	default:
>  		for (unsigned int i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
> diff --git a/lib/hash/rte_cuckoo_hash.c b/lib/hash/rte_cuckoo_hash.c
> index e41f03270a..7a474267f0 100644
> --- a/lib/hash/rte_cuckoo_hash.c
> +++ b/lib/hash/rte_cuckoo_hash.c
> @@ -452,6 +452,8 @@ rte_hash_create(const struct rte_hash_parameters *params)
>  #elif defined(RTE_ARCH_ARM64)
>  	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_NEON)) {
>  		h->sig_cmp_fn = RTE_HASH_COMPARE_NEON;
> +		if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SVE))
> +			h->sig_cmp_fn = RTE_HASH_COMPARE_SVE;

The RTE_HASH_COMPARE_SVE was defined in "PATCH v6 1/4] hash: pack the hitmask for hash in bulk lookup",
but its first use is in this commit, so I think it should defined in this commit.

If RTE_CPUFLAG_SVE and RTE_HAS_SVE_ACLE both set, then SVE impl will be chosen.
If RTE_CPUFLAG_SVE defined, but RTE_HAS_SVE_ACLE was not, then scalar will be chosen. --- in this case we could back to NEON impl.
So I suggest direct use "#if defined(RTE_HAS_SVE_ACLE)" here.

>  	}
>  	else
>  #endif
> 

Plus:
I notice the commit log said the SVE performance is slower than NEON.

And I also notice other platform SVE also lower than NEON,
1. b4ee9c07bd config/arm: disable SVE ACLE for CN10K
2. 4eea7c6461 config/arm: add SVE ACLE control flag

So maybe we should disable RTE_HAS_SVE_ACLE default by:
diff --git a/config/arm/meson.build b/config/arm/meson.build
index 9d6fb87d7f..a5b890d100 100644
--- a/config/arm/meson.build
+++ b/config/arm/meson.build
@@ -875,7 +875,7 @@ endif

 if cc.get_define('__ARM_FEATURE_SVE', args: machine_args) != ''
     compile_time_cpuflags += ['RTE_CPUFLAG_SVE']
-    if (cc.check_header('arm_sve.h') and soc_config.get('sve_acle', true))
+    if (cc.check_header('arm_sve.h') and soc_config.get('sve_acle', false))
         dpdk_conf.set('RTE_HAS_SVE_ACLE', 1)
     endif
 endif

If the platform verify SVE has higher performance, then it could enable SVE by add "sve_acle: true" in soc_xxx config.

Thanks