Add sbgemv_t_bfdot kernel for ARM64

This improves performance for sbgemv_t by up to 100x on NEOVERSEV1.
The geometric mean speedup is ~61x for M=N=[2,512].

CONTRIBUTORS.md

@@ -236,6 +236,7 @@ In chronological order:
 * Annop Wongwathanarat <annop.wongwathanarat@arm.com>
   * [2025-01-10] Add thread throttling profile for SGEMM on NEOVERSEV1
   * [2025-01-21] Optimize gemv_t_sve_v1x3 kernel
+  * [2025-02-26] Add sbgemv_t_bfdot kernel
 
 * Marek Michalowski <marek.michalowski@arm.com>
   * [2025-01-21] Add thread throttling profile for SGEMV on `NEOVERSEV1`

kernel/arm64/KERNEL.NEOVERSEN2

@@ -198,3 +198,4 @@ SBGEMMINCOPYOBJ =  sbgemm_incopy$(TSUFFIX).$(SUFFIX)
 SBGEMMITCOPYOBJ =  sbgemm_itcopy$(TSUFFIX).$(SUFFIX)
 SBGEMMONCOPYOBJ =  sbgemm_oncopy$(TSUFFIX).$(SUFFIX)
 SBGEMMOTCOPYOBJ =  sbgemm_otcopy$(TSUFFIX).$(SUFFIX)
+SBGEMVTKERNEL = sbgemv_t_bfdot.c

kernel/arm64/KERNEL.NEOVERSEV1

@@ -15,4 +15,5 @@ SBGEMMONCOPY    = sbgemm_ncopy_$(SBGEMM_UNROLL_N)_neoversev1.c
 SBGEMMOTCOPY    = sbgemm_tcopy_$(SBGEMM_UNROLL_N)_neoversev1.c
 SBGEMMONCOPYOBJ =  sbgemm_oncopy$(TSUFFIX).$(SUFFIX)
 SBGEMMOTCOPYOBJ =  sbgemm_otcopy$(TSUFFIX).$(SUFFIX)
+SBGEMVTKERNEL = sbgemv_t_bfdot.c
 endif

kernel/arm64/KERNEL.NEOVERSEV2

@@ -1 +1,5 @@
 include $(KERNELDIR)/KERNEL.ARMV8SVE
+
+ifeq ($(BUILD_BFLOAT16), 1)
+SBGEMVTKERNEL = sbgemv_t_bfdot.c
+endif

kernel/arm64/sbgemv_t_bfdot.c

@@ -0,0 +1,207 @@
+/***************************************************************************
+Copyright (c) 2025, The OpenBLAS Project
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   1. Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+   2. Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in
+      the documentation and/or other materials provided with the
+      distribution.
+   3. Neither the name of the OpenBLAS project nor the names of
+      its contributors may be used to endorse or promote products
+      derived from this software without specific prior written
+      permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*****************************************************************************/
+
+#include <arm_neon.h>
+#include "common.h"
+
+static inline float bf16_to_fp32(bfloat16 bf16) {
+  uint32_t fp32 = (uint32_t)bf16 << 16;
+  return *((float*)&fp32);
+}
+
+int CNAME(BLASLONG m, BLASLONG n, float alpha, bfloat16 *a, BLASLONG lda, bfloat16 *x, BLASLONG incx, float beta, float *y, BLASLONG incy)
+{
+  if (m < 1 || n < 1) return(0);
+  BLASLONG i;
+  BLASLONG ix,iy;
+  BLASLONG j;
+  bfloat16_t *a_ptr;
+  bfloat16_t *x_ptr;
+  float *y_ptr;
+  float temp;
+
+  iy = 0;
+  a_ptr = (bfloat16_t*)(a);
+  x_ptr = (bfloat16_t*)(x);
+
+  if (incx == 1) {
+    BLASLONG width = n / 4;
+
+    bfloat16_t *a0_ptr = a_ptr + lda * width * 0;
+    bfloat16_t *a1_ptr = a_ptr + lda * width * 1;
+    bfloat16_t *a2_ptr = a_ptr + lda * width * 2;
+    bfloat16_t *a3_ptr = a_ptr + lda * width * 3;
+
+    float *y0_ptr = y + incy * width * 0;
+    float *y1_ptr = y + incy * width * 1;
+    float *y2_ptr = y + incy * width * 2;
+    float *y3_ptr = y + incy * width * 3;
+
+    for (j = 0; j < width; j++) {
+      float32x4_t temp0_vec = vdupq_n_f32(0.0f);
+      float32x4_t temp1_vec = vdupq_n_f32(0.0f);
+      float32x4_t temp2_vec = vdupq_n_f32(0.0f);
+      float32x4_t temp3_vec = vdupq_n_f32(0.0f);
+
+      i = 0;
+      while (i + 7 < m) {
+        bfloat16x8_t x_vec = vld1q_bf16(x_ptr + i);
+
+        bfloat16x8_t a0_vec = vld1q_bf16(a0_ptr + i);
+        bfloat16x8_t a1_vec = vld1q_bf16(a1_ptr + i);
+        bfloat16x8_t a2_vec = vld1q_bf16(a2_ptr + i);
+        bfloat16x8_t a3_vec = vld1q_bf16(a3_ptr + i);
+
+        temp0_vec = vbfdotq_f32(temp0_vec, a0_vec, x_vec);
+        temp1_vec = vbfdotq_f32(temp1_vec, a1_vec, x_vec);
+        temp2_vec = vbfdotq_f32(temp2_vec, a2_vec, x_vec);
+        temp3_vec = vbfdotq_f32(temp3_vec, a3_vec, x_vec);
+
+        i += 8;
+      }
+      if (i + 3 < m) {
+        float32x2_t t0 = vdup_n_f32(0.0f);
+        float32x2_t t1 = vdup_n_f32(0.0f);
+        float32x2_t t2 = vdup_n_f32(0.0f);
+        float32x2_t t3 = vdup_n_f32(0.0f);
+
+        bfloat16x4_t x_vec = vld1_bf16(x_ptr + i);
+
+        bfloat16x4_t a0_vec = vld1_bf16(a0_ptr + i);
+        bfloat16x4_t a1_vec = vld1_bf16(a1_ptr + i);
+        bfloat16x4_t a2_vec = vld1_bf16(a2_ptr + i);
+        bfloat16x4_t a3_vec = vld1_bf16(a3_ptr + i);
+
+        t0 = vbfdot_f32(t0, a0_vec, x_vec);
+        t1 = vbfdot_f32(t1, a1_vec, x_vec);
+        t2 = vbfdot_f32(t2, a2_vec, x_vec);
+        t3 = vbfdot_f32(t3, a3_vec, x_vec);
+
+        float32x2_t temp0_vec_low = vget_low_f32(temp0_vec);
+        float32x2_t temp1_vec_low = vget_low_f32(temp1_vec);
+        float32x2_t temp2_vec_low = vget_low_f32(temp2_vec);
+        float32x2_t temp3_vec_low = vget_low_f32(temp3_vec);
+
+        temp0_vec = vcombine_f32(vadd_f32(t0, temp0_vec_low), vget_high_f32(temp0_vec));
+        temp1_vec = vcombine_f32(vadd_f32(t1, temp1_vec_low), vget_high_f32(temp1_vec));
+        temp2_vec = vcombine_f32(vadd_f32(t2, temp2_vec_low), vget_high_f32(temp2_vec));
+        temp3_vec = vcombine_f32(vadd_f32(t3, temp3_vec_low), vget_high_f32(temp3_vec));
+
+        i += 4;
+      }
+      if (beta == 0.0f) {
+        y0_ptr[iy] = alpha * vaddvq_f32(temp0_vec);
+        y1_ptr[iy] = alpha * vaddvq_f32(temp1_vec);
+        y2_ptr[iy] = alpha * vaddvq_f32(temp2_vec);
+        y3_ptr[iy] = alpha * vaddvq_f32(temp3_vec);
+      }
+      else {
+        y0_ptr[iy] = alpha * vaddvq_f32(temp0_vec) + beta * y0_ptr[iy];
+        y1_ptr[iy] = alpha * vaddvq_f32(temp1_vec) + beta * y1_ptr[iy];
+        y2_ptr[iy] = alpha * vaddvq_f32(temp2_vec) + beta * y2_ptr[iy];
+        y3_ptr[iy] = alpha * vaddvq_f32(temp3_vec) + beta * y3_ptr[iy];
+      }
+
+      for (; i < m; ++i) {
+        y0_ptr[iy] += alpha * a0_ptr[i] * x_ptr[i];
+        y1_ptr[iy] += alpha * a1_ptr[i] * x_ptr[i];
+        y2_ptr[iy] += alpha * a2_ptr[i] * x_ptr[i];
+        y3_ptr[iy] += alpha * a3_ptr[i] * x_ptr[i];
+      }
+
+      iy += incy;
+
+      a0_ptr += lda;
+      a1_ptr += lda;
+      a2_ptr += lda;
+      a3_ptr += lda;
+    }
+
+    a_ptr = a3_ptr;
+    y_ptr = y3_ptr;
+    for (j = width * 4; j < n; j++) {
+      float32x4_t temp0_vec = vdupq_n_f32(0.0f);
+      i = 0;
+      while (i + 7 < m) {
+        bfloat16x8_t x_vec = vld1q_bf16(x_ptr + i);
+        bfloat16x8_t a0_vec = vld1q_bf16(a_ptr + i);
+        temp0_vec = vbfdotq_f32(temp0_vec, a0_vec, x_vec);
+
+        i += 8;
+      }
+      if (i + 3 < m) {
+        float32x2_t t0 = vdup_n_f32(0.0f);
+        bfloat16x4_t x_vec = vld1_bf16(x_ptr + i);
+        bfloat16x4_t a0_vec = vld1_bf16(a_ptr + i);
+
+        t0 = vbfdot_f32(t0, a0_vec, x_vec);
+        float32x2_t temp0_vec_low = vget_low_f32(temp0_vec);
+        temp0_vec = vcombine_f32(vadd_f32(t0, temp0_vec_low), vget_high_f32(temp0_vec));
+
+        i += 4;
+      }
+      if (beta == 0.0f) {
+        y_ptr[iy] = alpha * vaddvq_f32(temp0_vec);
+      }
+      else {
+        y_ptr[iy] = alpha * vaddvq_f32(temp0_vec) + beta * y_ptr[iy];
+      }
+
+      for (; i < m; ++i) {
+        y_ptr[iy] += alpha * a_ptr[i] * x_ptr[i];
+      }
+
+      iy += incy;
+
+      a_ptr += lda;
+    }
+    return(0);
+  }
+
+  for (j = 0; j < n; j++) {
+    temp = 0.0;
+    ix = 0;
+    for (i = 0; i < m; i++) {
+      temp += bf16_to_fp32(a[i]) * bf16_to_fp32(x[ix]);
+      ix += incx;
+    }
+    if (beta == 0.0f) {
+      y[iy] = alpha * temp;
+    }
+    else {
+      y[iy] = alpha * temp + beta * y[iy];
+    }
+    iy += incy;
+    a += lda;
+  }
+  return (0);
+}