1 /* 2 * Simple C functions to supplement the C library 3 * 4 * Copyright (c) 2006 Fabrice Bellard 5 * 6 * Permission is hereby granted, free of charge, to any person obtaining a copy 7 * of this software and associated documentation files (the "Software"), to deal 8 * in the Software without restriction, including without limitation the rights 9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 10 * copies of the Software, and to permit persons to whom the Software is 11 * furnished to do so, subject to the following conditions: 12 * 13 * The above copyright notice and this permission notice shall be included in 14 * all copies or substantial portions of the Software. 15 * 16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 22 * THE SOFTWARE. 23 */ 24 #include "qemu/osdep.h" 25 #include "qemu/cutils.h" 26 #include "qemu/bswap.h" 27 #include "host/cpuinfo.h" 28 29 static bool 30 buffer_zero_int(const void *buf, size_t len) 31 { 32 if (unlikely(len < 8)) { 33 /* For a very small buffer, simply accumulate all the bytes. */ 34 const unsigned char *p = buf; 35 const unsigned char *e = buf + len; 36 unsigned char t = 0; 37 38 do { 39 t |= *p++; 40 } while (p < e); 41 42 return t == 0; 43 } else { 44 /* Otherwise, use the unaligned memory access functions to 45 handle the beginning and end of the buffer, with a couple 46 of loops handling the middle aligned section. */ 47 uint64_t t = ldq_he_p(buf); 48 const uint64_t *p = (uint64_t *)(((uintptr_t)buf + 8) & -8); 49 const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8); 50 51 for (; p + 8 <= e; p += 8) { 52 __builtin_prefetch(p + 8); 53 if (t) { 54 return false; 55 } 56 t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7]; 57 } 58 while (p < e) { 59 t |= *p++; 60 } 61 t |= ldq_he_p(buf + len - 8); 62 63 return t == 0; 64 } 65 } 66 67 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT) || defined(__SSE2__) 68 #include <immintrin.h> 69 70 /* Note that each of these vectorized functions require len >= 64. */ 71 72 static bool __attribute__((target("sse2"))) 73 buffer_zero_sse2(const void *buf, size_t len) 74 { 75 __m128i t = _mm_loadu_si128(buf); 76 __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16); 77 __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16); 78 __m128i zero = _mm_setzero_si128(); 79 80 /* Loop over 16-byte aligned blocks of 64. */ 81 while (likely(p <= e)) { 82 __builtin_prefetch(p); 83 t = _mm_cmpeq_epi8(t, zero); 84 if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) { 85 return false; 86 } 87 t = p[-4] | p[-3] | p[-2] | p[-1]; 88 p += 4; 89 } 90 91 /* Finish the aligned tail. */ 92 t |= e[-3]; 93 t |= e[-2]; 94 t |= e[-1]; 95 96 /* Finish the unaligned tail. */ 97 t |= _mm_loadu_si128(buf + len - 16); 98 99 return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF; 100 } 101 102 #ifdef CONFIG_AVX2_OPT 103 static bool __attribute__((target("avx2"))) 104 buffer_zero_avx2(const void *buf, size_t len) 105 { 106 /* Begin with an unaligned head of 32 bytes. */ 107 __m256i t = _mm256_loadu_si256(buf); 108 __m256i *p = (__m256i *)(((uintptr_t)buf + 5 * 32) & -32); 109 __m256i *e = (__m256i *)(((uintptr_t)buf + len) & -32); 110 111 /* Loop over 32-byte aligned blocks of 128. */ 112 while (p <= e) { 113 __builtin_prefetch(p); 114 if (unlikely(!_mm256_testz_si256(t, t))) { 115 return false; 116 } 117 t = p[-4] | p[-3] | p[-2] | p[-1]; 118 p += 4; 119 } ; 120 121 /* Finish the last block of 128 unaligned. */ 122 t |= _mm256_loadu_si256(buf + len - 4 * 32); 123 t |= _mm256_loadu_si256(buf + len - 3 * 32); 124 t |= _mm256_loadu_si256(buf + len - 2 * 32); 125 t |= _mm256_loadu_si256(buf + len - 1 * 32); 126 127 return _mm256_testz_si256(t, t); 128 } 129 #endif /* CONFIG_AVX2_OPT */ 130 131 #ifdef CONFIG_AVX512F_OPT 132 static bool __attribute__((target("avx512f"))) 133 buffer_zero_avx512(const void *buf, size_t len) 134 { 135 /* Begin with an unaligned head of 64 bytes. */ 136 __m512i t = _mm512_loadu_si512(buf); 137 __m512i *p = (__m512i *)(((uintptr_t)buf + 5 * 64) & -64); 138 __m512i *e = (__m512i *)(((uintptr_t)buf + len) & -64); 139 140 /* Loop over 64-byte aligned blocks of 256. */ 141 while (p <= e) { 142 __builtin_prefetch(p); 143 if (unlikely(_mm512_test_epi64_mask(t, t))) { 144 return false; 145 } 146 t = p[-4] | p[-3] | p[-2] | p[-1]; 147 p += 4; 148 } 149 150 t |= _mm512_loadu_si512(buf + len - 4 * 64); 151 t |= _mm512_loadu_si512(buf + len - 3 * 64); 152 t |= _mm512_loadu_si512(buf + len - 2 * 64); 153 t |= _mm512_loadu_si512(buf + len - 1 * 64); 154 155 return !_mm512_test_epi64_mask(t, t); 156 157 } 158 #endif /* CONFIG_AVX512F_OPT */ 159 160 /* 161 * Make sure that these variables are appropriately initialized when 162 * SSE2 is enabled on the compiler command-line, but the compiler is 163 * too old to support CONFIG_AVX2_OPT. 164 */ 165 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT) 166 # define INIT_USED 0 167 # define INIT_LENGTH 0 168 # define INIT_ACCEL buffer_zero_int 169 #else 170 # ifndef __SSE2__ 171 # error "ISA selection confusion" 172 # endif 173 # define INIT_USED CPUINFO_SSE2 174 # define INIT_LENGTH 64 175 # define INIT_ACCEL buffer_zero_sse2 176 #endif 177 178 static unsigned used_accel = INIT_USED; 179 static unsigned length_to_accel = INIT_LENGTH; 180 static bool (*buffer_accel)(const void *, size_t) = INIT_ACCEL; 181 182 static unsigned __attribute__((noinline)) 183 select_accel_cpuinfo(unsigned info) 184 { 185 /* Array is sorted in order of algorithm preference. */ 186 static const struct { 187 unsigned bit; 188 unsigned len; 189 bool (*fn)(const void *, size_t); 190 } all[] = { 191 #ifdef CONFIG_AVX512F_OPT 192 { CPUINFO_AVX512F, 256, buffer_zero_avx512 }, 193 #endif 194 #ifdef CONFIG_AVX2_OPT 195 { CPUINFO_AVX2, 128, buffer_zero_avx2 }, 196 #endif 197 { CPUINFO_SSE2, 64, buffer_zero_sse2 }, 198 { CPUINFO_ALWAYS, 0, buffer_zero_int }, 199 }; 200 201 for (unsigned i = 0; i < ARRAY_SIZE(all); ++i) { 202 if (info & all[i].bit) { 203 length_to_accel = all[i].len; 204 buffer_accel = all[i].fn; 205 return all[i].bit; 206 } 207 } 208 return 0; 209 } 210 211 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT) 212 static void __attribute__((constructor)) init_accel(void) 213 { 214 used_accel = select_accel_cpuinfo(cpuinfo_init()); 215 } 216 #endif /* CONFIG_AVX2_OPT */ 217 218 bool test_buffer_is_zero_next_accel(void) 219 { 220 /* 221 * Accumulate the accelerators that we've already tested, and 222 * remove them from the set to test this round. We'll get back 223 * a zero from select_accel_cpuinfo when there are no more. 224 */ 225 unsigned used = select_accel_cpuinfo(cpuinfo & ~used_accel); 226 used_accel |= used; 227 return used; 228 } 229 230 static bool select_accel_fn(const void *buf, size_t len) 231 { 232 if (likely(len >= length_to_accel)) { 233 return buffer_accel(buf, len); 234 } 235 return buffer_zero_int(buf, len); 236 } 237 238 #else 239 #define select_accel_fn buffer_zero_int 240 bool test_buffer_is_zero_next_accel(void) 241 { 242 return false; 243 } 244 #endif 245 246 /* 247 * Checks if a buffer is all zeroes 248 */ 249 bool buffer_is_zero(const void *buf, size_t len) 250 { 251 if (unlikely(len == 0)) { 252 return true; 253 } 254 255 /* Fetch the beginning of the buffer while we select the accelerator. */ 256 __builtin_prefetch(buf); 257 258 /* Use an optimized zero check if possible. Note that this also 259 includes a check for an unrolled loop over 64-bit integers. */ 260 return select_accel_fn(buf, len); 261 } 262