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Enable SVE Support for L2 Metric Computation in FP32 #969

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19 changes: 16 additions & 3 deletions cmake/libs/libfaiss.cmake
Original file line number Diff line number Diff line change
Expand Up @@ -47,12 +47,25 @@ if(__X86_64)
endif()

if(__AARCH64)
set(UTILS_SRC src/simd/hook.cc src/simd/distances_ref.cc
src/simd/distances_neon.cc)
add_library(knowhere_utils STATIC ${UTILS_SRC})

set(UTILS_SRC src/simd/distances_ref.cc src/simd/distances_neon.cc)
set(UTILS_SVE_SRC src/simd/hook.cc src/simd/distances_sve.cc)
set(ALL_UTILS_SRC ${UTILS_SRC} ${UTILS_SVE_SRC})
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You can directly place the SVE source file into the UTILS_SRC variable.

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If all four files are compiled with the +sve tag and only UTILS_SRC is used, there will be an issue with illegal instructions on NEON machines. This is because the code will be compiled specifically for SVE instructions as compiler will recognize the instructions, which NEON machines cannot execute, leading to a failure in running the compiled code.


add_library(
knowhere_utils STATIC
${ALL_UTILS_SRC}
)

foreach(SVE_FILE ${UTILS_SVE_SRC})
set_source_files_properties(${SVE_FILE} PROPERTIES COMPILE_OPTIONS "-march=armv8-a+sve")
endforeach()

target_compile_options(knowhere_utils PRIVATE -march=armv8-a)
target_link_libraries(knowhere_utils PUBLIC glog::glog)
endif()


# ToDo: Add distances_vsx.cc for powerpc64 SIMD acceleration
if(__PPC64)
set(UTILS_SRC src/simd/hook.cc src/simd/distances_ref.cc src/simd/distances_powerpc.cc)
Expand Down
184 changes: 184 additions & 0 deletions src/simd/distances_sve.cc
Original file line number Diff line number Diff line change
@@ -0,0 +1,184 @@
// Copyright (C) 2019-2023 Zilliz. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software distributed under the License
// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
// or implied. See the License for the specific language governing permissions and limitations under the License.

#include "distances_sve.h"

#include <arm_sve.h>

#include <cmath>

#include "faiss/impl/platform_macros.h"
#if defined(__ARM_FEATURE_SVE)
namespace faiss {

float
fvec_L2sqr_sve(const float* x, const float* y, size_t d) {
svfloat32_t sum = svdup_f32(0.0f);
size_t i = 0;

svbool_t pg = svptrue_b32();

while (i < d) {
if (d - i < svcntw())
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I believe that this if condition is not needed, just pg = svwhilelt_b32(i, d); should be sufficient

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Thank you so much, @alexanderguzhva , for the valuable suggestions. During development, we considered this approach as well, and our reason for going with the current approach is as follows:

Using the if condition to update pg only in the last iteration avoids unnecessary updates and reduces the dependency chain introduced by the svwhilelt instruction. This optimization minimizes stalls caused by these dependencies, allowing the processor pipeline to operate more efficiently.

pg = svwhilelt_b32(i, d);

svfloat32_t a = svld1_f32(pg, x + i);
svfloat32_t b = svld1_f32(pg, y + i);
svfloat32_t diff = svsub_f32_m(pg, a, b);
sum = svmla_f32_m(pg, sum, diff, diff);
i += svcntw();
}

return svaddv_f32(svptrue_b32(), sum);
}

float
fvec_L1_sve(const float* x, const float* y, size_t d) {
svfloat32_t sum = svdup_f32(0.0f);
size_t i = 0;

svbool_t pg = svptrue_b32();

while (i < d) {
if (d - i < svcntw())
pg = svwhilelt_b32(i, d);

svfloat32_t a = svld1_f32(pg, x + i);
svfloat32_t b = svld1_f32(pg, y + i);
svfloat32_t diff = svabs_f32_x(pg, svsub_f32_m(pg, a, b));
sum = svadd_f32_m(pg, sum, diff);
i += svcntw();
}

return svaddv_f32(svptrue_b32(), sum);
}

float
fvec_Linf_sve(const float* x, const float* y, size_t d) {
svfloat32_t max_val = svdup_f32(0.0f);
size_t i = 0;

svbool_t pg = svptrue_b32();

while (i < d) {
if (d - i < svcntw())
pg = svwhilelt_b32(i, d);

svfloat32_t a = svld1_f32(pg, x + i);
svfloat32_t b = svld1_f32(pg, y + i);
svfloat32_t diff = svabs_f32_x(pg, svsub_f32_m(pg, a, b));
max_val = svmax_f32_m(pg, max_val, diff);
i += svcntw();
}

return svmaxv_f32(svptrue_b32(), max_val);
}

float
fvec_norm_L2sqr_sve(const float* x, size_t d) {
svfloat32_t sum = svdup_f32(0.0f);
size_t i = 0;

svbool_t pg = svptrue_b32();

while (i < d) {
if (d - i < svcntw())
pg = svwhilelt_b32(i, d);

svfloat32_t a = svld1_f32(pg, x + i);
sum = svmla_f32_m(pg, sum, a, a);
i += svcntw();
}

return svaddv_f32(svptrue_b32(), sum);
}

void
fvec_madd_sve(size_t n, const float* a, float bf, const float* b, float* c) {
size_t i = 0;
svfloat32_t bf_vec = svdup_f32(bf);

svbool_t pg = svptrue_b32();

while (i < n) {
if (n - i < svcntw())
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The handling of the tail block here could be more elegant, as SVE's predicate registers are inherently friendly to out-of-bounds memory access.

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#969 (comment)

During development, we considered this approach but ultimately chose the current method for the following reasons:

Using an if condition to update the predicate (pg) only in the last iteration avoids unnecessary updates and reduces the dependency chain introduced by the svwhilelt instruction. This optimization minimizes pipeline stalls caused by these dependencies, enabling the processor to operate more efficiently.

pg = svwhilelt_b32(i, n);

svfloat32_t a_vec = svld1_f32(pg, a + i);
svfloat32_t b_vec = svld1_f32(pg, b + i);
svfloat32_t c_vec = svmla_f32_m(pg, a_vec, b_vec, bf_vec);
svst1_f32(pg, c + i, c_vec);
i += svcntw();
}
}

int
fvec_madd_and_argmin_sve(size_t n, const float* a, float bf, const float* b, float* c) {
size_t i = 0;
svfloat32_t min_val = svdup_f32(INFINITY);
svuint32_t min_idx = svdup_u32(0);
svuint32_t idx_base = svindex_u32(0, 1);

svfloat32_t bf_vec = svdup_f32(bf);
svbool_t pg = svptrue_b32();

while (i < n) {
if (n - i < svcntw())
pg = svwhilelt_b32(i, n);

svuint32_t idx = svadd_u32_z(pg, idx_base, svdup_u32(i));
svfloat32_t a_vec = svld1_f32(pg, a + i);
svfloat32_t b_vec = svld1_f32(pg, b + i);
svfloat32_t c_vec = svmla_f32_m(pg, a_vec, b_vec, bf_vec);
svst1_f32(pg, c + i, c_vec);

svbool_t cmp = svcmplt(pg, c_vec, min_val);
min_val = svsel_f32(cmp, c_vec, min_val);
min_idx = svsel_u32(cmp, idx, min_idx);

i += svcntw();
}

float min_value = svminv_f32(svptrue_b32(), min_val);
svbool_t pg_min = svcmpeq(svptrue_b32(), min_val, svdup_f32(min_value));
uint32_t min_index = svlastb_u32(pg_min, min_idx);

return static_cast<int>(min_index);
}

void
fvec_L2sqr_batch_4_sve(const float* x, const float* y0, const float* y1, const float* y2, const float* y3,
const size_t d, float& dis0, float& dis1, float& dis2, float& dis3) {
float d0 = 0;
float d1 = 0;
float d2 = 0;
float d3 = 0;

for (size_t i = 0; i < d; ++i) {
const float q0 = x[i] - y0[i];
const float q1 = x[i] - y1[i];
const float q2 = x[i] - y2[i];
const float q3 = x[i] - y3[i];
d0 += q0 * q0;
d1 += q1 * q1;
d2 += q2 * q2;
d3 += q3 * q3;
}

dis0 = d0;
dis1 = d1;
dis2 = d2;
dis3 = d3;
}

} // namespace faiss

#endif
45 changes: 45 additions & 0 deletions src/simd/distances_sve.h
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
// Copyright (C) 2019-2023 Zilliz. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software distributed under the License
// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
// or implied. See the License for the specific language governing permissions and limitations under the License.

#include <arm_sve.h>

#include <cstdint>
#include <cstdio>
#if defined(__ARM_FEATURE_SVE)
namespace faiss {

float
fvec_L2sqr_sve(const float* x, const float* y, size_t d);

float
fvec_L1_sve(const float* x, const float* y, size_t d);

float
fvec_Linf_sve(const float* x, const float* y, size_t d);

float
fvec_norm_L2sqr_sve(const float* x, size_t d);

void
fvec_madd_sve(size_t n, const float* a, float bf, const float* b, float* c);

int
fvec_madd_and_argmin_sve(size_t n, const float* a, float bf, const float* b, float* c);

int32_t
ivec_L2sqr_sve(const int8_t* x, const int8_t* y, size_t d);

void
fvec_L2sqr_batch_4_sve(const float* x, const float* y0, const float* y1, const float* y2, const float* y3,
const size_t d, float& dis0, float& dis1, float& dis2, float& dis3);

} // namespace faiss
#endif
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