Re: [PATCH v9 4/4] hash: add SVE support for bulk key lookup

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

On Tue, Apr 30, 2024 at 6:28 PM Yoan Picchi <yoan.picchi@arm.com> wrote:
>
> - Implemented SVE code for comparing signatures in bulk lookup.
> - New SVE code is ~5% slower than optimized NEON for N2 processor for
> 128b vectors.
>
> Signed-off-by: Yoan Picchi <yoan.picchi@arm.com>
> Signed-off-by: Harjot Singh <harjot.singh@arm.com>
> Reviewed-by: Nathan Brown <nathan.brown@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> ---
>  lib/hash/arch/arm/compare_signatures.h | 58 ++++++++++++++++++++++++++
>  lib/hash/rte_cuckoo_hash.c             |  7 +++-
>  lib/hash/rte_cuckoo_hash.h             |  1 +
>  3 files changed, 65 insertions(+), 1 deletion(-)
>
> diff --git a/lib/hash/arch/arm/compare_signatures.h b/lib/hash/arch/arm/compare_signatures.h
> index 72bd171484..b4b4cf04e9 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: {
> +               svuint16_t vsign, shift, sv_matches;
> +               svbool_t pred, match, bucket_wide_pred;
> +               int i = 0;
> +               uint64_t vl = svcnth();
> +
> +               vsign = svdup_u16(sig);
> +               shift = svindex_u16(0, 1);
> +
> +               if (vl >= 2 * RTE_HASH_BUCKET_ENTRIES && RTE_HASH_BUCKET_ENTRIES <= 8) {
> +                       svuint16_t primary_array_vect, secondary_array_vect;
> +                       bucket_wide_pred = svwhilelt_b16(0, RTE_HASH_BUCKET_ENTRIES);
> +                       primary_array_vect = svld1_u16(bucket_wide_pred, prim_bucket_sigs);
> +                       secondary_array_vect = svld1_u16(bucket_wide_pred, sec_bucket_sigs);
> +
> +                       /* We merged the two vectors so we can do both comparisons at once */
> +                       primary_array_vect = svsplice_u16(bucket_wide_pred,
> +                               primary_array_vect,
> +                               secondary_array_vect);
> +                       pred = svwhilelt_b16(0, 2*RTE_HASH_BUCKET_ENTRIES);
> +
> +                       /* Compare all signatures in the buckets */
> +                       match = svcmpeq_u16(pred, vsign, primary_array_vect);
> +                       if (svptest_any(svptrue_b16(), match)) {
> +                               sv_matches = svdup_u16(1);
> +                               sv_matches = svlsl_u16_z(match, sv_matches, shift);
> +                               *hitmask_buffer = svorv_u16(svptrue_b16(), sv_matches);
> +                       }
> +               } else {
> +                       do {
> +                               pred = svwhilelt_b16(i, RTE_HASH_BUCKET_ENTRIES);
> +                               uint16_t lower_half = 0;
> +                               uint16_t upper_half = 0;
> +                               /* Compare all signatures in the primary bucket */
> +                               match = svcmpeq_u16(pred, vsign, svld1_u16(pred,
> +                                                       &prim_bucket_sigs[i]));
> +                               if (svptest_any(svptrue_b16(), match)) {
> +                                       sv_matches = svdup_u16(1);
> +                                       sv_matches = svlsl_u16_z(match, sv_matches, shift);
> +                                       lower_half = svorv_u16(svptrue_b16(), sv_matches);
> +                               }
> +                               /* Compare all signatures in the secondary bucket */
> +                               match = svcmpeq_u16(pred, vsign, svld1_u16(pred,
> +                                                       &sec_bucket_sigs[i]));
> +                               if (svptest_any(svptrue_b16(), match)) {
> +                                       sv_matches = svdup_u16(1);
> +                                       sv_matches = svlsl_u16_z(match, sv_matches, shift);
> +                                       upper_half = svorv_u16(svptrue_b16(), sv_matches)
> +                                               << RTE_HASH_BUCKET_ENTRIES;
> +                               }
> +                               hitmask_buffer[i / 8] = upper_half | lower_half;
> +                               i += vl;
> +                       } while (i < RTE_HASH_BUCKET_ENTRIES);
> +               }
> +               }
> +               break;
>  #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 0697743cdf..75f555ba2c 100644
> --- a/lib/hash/rte_cuckoo_hash.c
> +++ b/lib/hash/rte_cuckoo_hash.c
> @@ -450,8 +450,13 @@ rte_hash_create(const struct rte_hash_parameters *params)
>                 h->sig_cmp_fn = RTE_HASH_COMPARE_SSE;
>         else
>  #elif defined(RTE_ARCH_ARM64)
> -       if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_NEON))
> +       if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_NEON)) {
>                 h->sig_cmp_fn = RTE_HASH_COMPARE_NEON;
> +#if defined(RTE_HAS_SVE_ACLE)
> +               if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SVE))
> +                       h->sig_cmp_fn = RTE_HASH_COMPARE_SVE;
> +#endif
> +       }
>         else
>  #endif
>                 h->sig_cmp_fn = RTE_HASH_COMPARE_SCALAR;
> diff --git a/lib/hash/rte_cuckoo_hash.h b/lib/hash/rte_cuckoo_hash.h
> index a528f1d1a0..01ad01c258 100644
> --- a/lib/hash/rte_cuckoo_hash.h
> +++ b/lib/hash/rte_cuckoo_hash.h
> @@ -139,6 +139,7 @@ enum rte_hash_sig_compare_function {
>         RTE_HASH_COMPARE_SCALAR = 0,
>         RTE_HASH_COMPARE_SSE,
>         RTE_HASH_COMPARE_NEON,
> +       RTE_HASH_COMPARE_SVE,
>         RTE_HASH_COMPARE_NUM
>  };

I am surprised the ABI check does not complain over this change.
RTE_HASH_COMPARE_NUM is not used and knowing the number of compare
function implementations should not be of interest for an application.
But it still seem an ABI breakage to me.

RTE_HASH_COMPARE_NUM can be removed in v24.11.
And ideally, sig_cmp_fn should be made opaque (or moved to an opaque
struct out of the rte_hash public struct).


-- 
David Marchand