Re: [PATCH v9 1/4] hash: pack the hitmask for hash in bulk lookup

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

On Tue, Apr 30, 2024 at 6:28 PM Yoan Picchi <yoan.picchi@arm.com> wrote:
>
> Current hitmask includes padding due to Intel's SIMD
> implementation detail. This patch allows non Intel SIMD
> implementations to benefit from a dense hitmask.
> In addition, the new dense hitmask interweave the primary
> and secondary matches which allow a better cache usage and
> enable future improvements for the SIMD implementations
> The default non SIMD path now use this dense mask.
>
> Signed-off-by: Yoan Picchi <yoan.picchi@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> Reviewed-by: Nathan Brown <nathan.brown@arm.com>
> ---
>  .mailmap                                  |   2 +
>  lib/hash/arch/arm/compare_signatures.h    |  61 +++++++
>  lib/hash/arch/common/compare_signatures.h |  37 +++++
>  lib/hash/arch/x86/compare_signatures.h    |  53 ++++++
>  lib/hash/rte_cuckoo_hash.c                | 192 ++++++++++++----------
>  5 files changed, 254 insertions(+), 91 deletions(-)
>  create mode 100644 lib/hash/arch/arm/compare_signatures.h
>  create mode 100644 lib/hash/arch/common/compare_signatures.h
>  create mode 100644 lib/hash/arch/x86/compare_signatures.h
>
> diff --git a/.mailmap b/.mailmap
> index 66ebc20666..00b50414d3 100644
> --- a/.mailmap
> +++ b/.mailmap
> @@ -494,6 +494,7 @@ Hari Kumar Vemula <hari.kumarx.vemula@intel.com>
>  Harini Ramakrishnan <harini.ramakrishnan@microsoft.com>
>  Hariprasad Govindharajan <hariprasad.govindharajan@intel.com>
>  Harish Patil <harish.patil@cavium.com> <harish.patil@qlogic.com>
> +Harjot Singh <harjot.singh@arm.com>

This should be in patch 3.


>  Harman Kalra <hkalra@marvell.com>
>  Harneet Singh <harneet.singh@intel.com>
>  Harold Huang <baymaxhuang@gmail.com>
> @@ -1633,6 +1634,7 @@ Yixue Wang <yixue.wang@intel.com>
>  Yi Yang <yangyi01@inspur.com> <yi.y.yang@intel.com>
>  Yi Zhang <zhang.yi75@zte.com.cn>
>  Yoann Desmouceaux <ydesmouc@cisco.com>
> +Yoan Picchi <yoan.picchi@arm.com>
>  Yogesh Jangra <yogesh.jangra@intel.com>
>  Yogev Chaimovich <yogev@cgstowernetworks.com>
>  Yongjie Gu <yongjiex.gu@intel.com>
> diff --git a/lib/hash/arch/arm/compare_signatures.h b/lib/hash/arch/arm/compare_signatures.h
> new file mode 100644
> index 0000000000..46d15da89f
> --- /dev/null
> +++ b/lib/hash/arch/arm/compare_signatures.h

Why create a new directory?

Simple lib/hash/hash_compare_signature_{arm,x86,generic}.h are enough.


> @@ -0,0 +1,61 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2010-2016 Intel Corporation
> + * Copyright(c) 2018-2024 Arm Limited
> + */
> +
> +/*
> + * Arm's version uses a densely packed hitmask buffer:
> + * Every bit is in use.
> + */
> +
> +#include <inttypes.h>
> +#include <rte_common.h>
> +#include <rte_vect.h>
> +#include "rte_cuckoo_hash.h"

Please separate headers by groups, like in
https://doc.dpdk.org/guides/contributing/coding_style.html#header-includes

> +
> +#define DENSE_HASH_BULK_LOOKUP 1
> +
> +static inline void
> +compare_signatures_dense(uint16_t *hitmask_buffer,
> +                       const uint16_t *prim_bucket_sigs,
> +                       const uint16_t *sec_bucket_sigs,
> +                       uint16_t sig,
> +                       enum rte_hash_sig_compare_function sig_cmp_fn)

Strange indent.

> +{
> +
> +       static_assert(sizeof(*hitmask_buffer) >= 2 * (RTE_HASH_BUCKET_ENTRIES / 8),
> +                                 "hitmask_buffer must be wide enough to fit a dense hitmask");

This is similar but less strict than an added check in
rte_cuckoo_hash.c later in this patch.
So I suspect only one of those checks is necessary.
But I don't understand the logic, so for you to figure out :-).


> +
> +       /* For match mask every bits indicates the match */
> +       switch (sig_cmp_fn) {
> +#if RTE_HASH_BUCKET_ENTRIES <= 8
> +       case RTE_HASH_COMPARE_NEON: {
> +               uint16x8_t vmat, vsig, x;
> +               int16x8_t shift = {0, 1, 2, 3, 4, 5, 6, 7};
> +               uint16_t low, high;
> +
> +               vsig = vld1q_dup_u16((uint16_t const *)&sig);
> +               /* Compare all signatures in the primary bucket */
> +               vmat = vceqq_u16(vsig,
> +                       vld1q_u16((uint16_t const *)prim_bucket_sigs));

General comment for this series.
When possible, keep on the same line up to 100 chars, the code is hard
enough to read with all those vector intrinsics...


> +               x = vshlq_u16(vandq_u16(vmat, vdupq_n_u16(0x0001)), shift);
> +               low = (uint16_t)(vaddvq_u16(x));
> +               /* Compare all signatures in the secondary bucket */
> +               vmat = vceqq_u16(vsig,
> +                       vld1q_u16((uint16_t const *)sec_bucket_sigs));
> +               x = vshlq_u16(vandq_u16(vmat, vdupq_n_u16(0x0001)), shift);
> +               high = (uint16_t)(vaddvq_u16(x));
> +               *hitmask_buffer = low | high << RTE_HASH_BUCKET_ENTRIES;
> +
> +               }
> +               break;
> +#endif
> +       default:
> +               for (unsigned int i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
> +                       *hitmask_buffer |=
> +                               (sig == prim_bucket_sigs[i]) << i;
> +                       *hitmask_buffer |=
> +                               ((sig == sec_bucket_sigs[i]) << i) << RTE_HASH_BUCKET_ENTRIES;
> +               }
> +       }
> +}

[snip]


-- 
David Marchand