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 28 static bool 29 buffer_zero_int(const void *buf, size_t len) 30 { 31 if (unlikely(len < 8)) { 32 /* For a very small buffer, simply accumulate all the bytes. */ 33 const unsigned char *p = buf; 34 const unsigned char *e = buf + len; 35 unsigned char t = 0; 36 37 do { 38 t |= *p++; 39 } while (p < e); 40 41 return t == 0; 42 } else { 43 /* Otherwise, use the unaligned memory access functions to 44 handle the beginning and end of the buffer, with a couple 45 of loops handling the middle aligned section. */ 46 uint64_t t = ldq_he_p(buf); 47 const uint64_t *p = (uint64_t *)(((uintptr_t)buf + 8) & -8); 48 const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8); 49 50 for (; p + 8 <= e; p += 8) { 51 __builtin_prefetch(p + 8); 52 if (t) { 53 return false; 54 } 55 t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7]; 56 } 57 while (p < e) { 58 t |= *p++; 59 } 60 t |= ldq_he_p(buf + len - 8); 61 62 return t == 0; 63 } 64 } 65 66 #if defined(CONFIG_AVX2_OPT) || defined(__SSE2__) 67 /* Do not use push_options pragmas unnecessarily, because clang 68 * does not support them. 69 */ 70 #ifdef CONFIG_AVX2_OPT 71 #pragma GCC push_options 72 #pragma GCC target("sse2") 73 #endif 74 #include <emmintrin.h> 75 76 /* Note that each of these vectorized functions require len >= 64. */ 77 78 static bool 79 buffer_zero_sse2(const void *buf, size_t len) 80 { 81 __m128i t = _mm_loadu_si128(buf); 82 __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16); 83 __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16); 84 __m128i zero = _mm_setzero_si128(); 85 86 /* Loop over 16-byte aligned blocks of 64. */ 87 while (likely(p <= e)) { 88 __builtin_prefetch(p); 89 t = _mm_cmpeq_epi8(t, zero); 90 if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) { 91 return false; 92 } 93 t = p[-4] | p[-3] | p[-2] | p[-1]; 94 p += 4; 95 } 96 97 /* Finish the aligned tail. */ 98 t |= e[-3]; 99 t |= e[-2]; 100 t |= e[-1]; 101 102 /* Finish the unaligned tail. */ 103 t |= _mm_loadu_si128(buf + len - 16); 104 105 return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF; 106 } 107 #ifdef CONFIG_AVX2_OPT 108 #pragma GCC pop_options 109 #endif 110 111 #ifdef CONFIG_AVX2_OPT 112 /* Note that due to restrictions/bugs wrt __builtin functions in gcc <= 4.8, 113 * the includes have to be within the corresponding push_options region, and 114 * therefore the regions themselves have to be ordered with increasing ISA. 115 */ 116 #pragma GCC push_options 117 #pragma GCC target("sse4") 118 #include <smmintrin.h> 119 120 static bool 121 buffer_zero_sse4(const void *buf, size_t len) 122 { 123 __m128i t = _mm_loadu_si128(buf); 124 __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16); 125 __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16); 126 127 /* Loop over 16-byte aligned blocks of 64. */ 128 while (likely(p <= e)) { 129 __builtin_prefetch(p); 130 if (unlikely(!_mm_testz_si128(t, t))) { 131 return false; 132 } 133 t = p[-4] | p[-3] | p[-2] | p[-1]; 134 p += 4; 135 } 136 137 /* Finish the aligned tail. */ 138 t |= e[-3]; 139 t |= e[-2]; 140 t |= e[-1]; 141 142 /* Finish the unaligned tail. */ 143 t |= _mm_loadu_si128(buf + len - 16); 144 145 return _mm_testz_si128(t, t); 146 } 147 148 #pragma GCC pop_options 149 #pragma GCC push_options 150 #pragma GCC target("avx2") 151 #include <immintrin.h> 152 153 static bool 154 buffer_zero_avx2(const void *buf, size_t len) 155 { 156 /* Begin with an unaligned head of 32 bytes. */ 157 __m256i t = _mm256_loadu_si256(buf); 158 __m256i *p = (__m256i *)(((uintptr_t)buf + 5 * 32) & -32); 159 __m256i *e = (__m256i *)(((uintptr_t)buf + len) & -32); 160 161 if (likely(p <= e)) { 162 /* Loop over 32-byte aligned blocks of 128. */ 163 do { 164 __builtin_prefetch(p); 165 if (unlikely(!_mm256_testz_si256(t, t))) { 166 return false; 167 } 168 t = p[-4] | p[-3] | p[-2] | p[-1]; 169 p += 4; 170 } while (p <= e); 171 } else { 172 t |= _mm256_loadu_si256(buf + 32); 173 if (len <= 128) { 174 goto last2; 175 } 176 } 177 178 /* Finish the last block of 128 unaligned. */ 179 t |= _mm256_loadu_si256(buf + len - 4 * 32); 180 t |= _mm256_loadu_si256(buf + len - 3 * 32); 181 last2: 182 t |= _mm256_loadu_si256(buf + len - 2 * 32); 183 t |= _mm256_loadu_si256(buf + len - 1 * 32); 184 185 return _mm256_testz_si256(t, t); 186 } 187 #pragma GCC pop_options 188 #endif /* CONFIG_AVX2_OPT */ 189 190 /* Note that for test_buffer_is_zero_next_accel, the most preferred 191 * ISA must have the least significant bit. 192 */ 193 #define CACHE_AVX2 1 194 #define CACHE_SSE4 2 195 #define CACHE_SSE2 4 196 197 /* Make sure that these variables are appropriately initialized when 198 * SSE2 is enabled on the compiler command-line, but the compiler is 199 * too old to support CONFIG_AVX2_OPT. 200 */ 201 #ifdef CONFIG_AVX2_OPT 202 # define INIT_CACHE 0 203 # define INIT_ACCEL buffer_zero_int 204 #else 205 # ifndef __SSE2__ 206 # error "ISA selection confusion" 207 # endif 208 # define INIT_CACHE CACHE_SSE2 209 # define INIT_ACCEL buffer_zero_sse2 210 #endif 211 212 static unsigned cpuid_cache = INIT_CACHE; 213 static bool (*buffer_accel)(const void *, size_t) = INIT_ACCEL; 214 215 static void init_accel(unsigned cache) 216 { 217 bool (*fn)(const void *, size_t) = buffer_zero_int; 218 if (cache & CACHE_SSE2) { 219 fn = buffer_zero_sse2; 220 } 221 #ifdef CONFIG_AVX2_OPT 222 if (cache & CACHE_SSE4) { 223 fn = buffer_zero_sse4; 224 } 225 if (cache & CACHE_AVX2) { 226 fn = buffer_zero_avx2; 227 } 228 #endif 229 buffer_accel = fn; 230 } 231 232 #ifdef CONFIG_AVX2_OPT 233 #include "qemu/cpuid.h" 234 235 static void __attribute__((constructor)) init_cpuid_cache(void) 236 { 237 int max = __get_cpuid_max(0, NULL); 238 int a, b, c, d; 239 unsigned cache = 0; 240 241 if (max >= 1) { 242 __cpuid(1, a, b, c, d); 243 if (d & bit_SSE2) { 244 cache |= CACHE_SSE2; 245 } 246 if (c & bit_SSE4_1) { 247 cache |= CACHE_SSE4; 248 } 249 250 /* We must check that AVX is not just available, but usable. */ 251 if ((c & bit_OSXSAVE) && (c & bit_AVX) && max >= 7) { 252 int bv; 253 __asm("xgetbv" : "=a"(bv), "=d"(d) : "c"(0)); 254 __cpuid_count(7, 0, a, b, c, d); 255 if ((bv & 6) == 6 && (b & bit_AVX2)) { 256 cache |= CACHE_AVX2; 257 } 258 } 259 } 260 cpuid_cache = cache; 261 init_accel(cache); 262 } 263 #endif /* CONFIG_AVX2_OPT */ 264 265 bool test_buffer_is_zero_next_accel(void) 266 { 267 /* If no bits set, we just tested buffer_zero_int, and there 268 are no more acceleration options to test. */ 269 if (cpuid_cache == 0) { 270 return false; 271 } 272 /* Disable the accelerator we used before and select a new one. */ 273 cpuid_cache &= cpuid_cache - 1; 274 init_accel(cpuid_cache); 275 return true; 276 } 277 278 static bool select_accel_fn(const void *buf, size_t len) 279 { 280 if (likely(len >= 64)) { 281 return buffer_accel(buf, len); 282 } 283 return buffer_zero_int(buf, len); 284 } 285 286 #else 287 #define select_accel_fn buffer_zero_int 288 bool test_buffer_is_zero_next_accel(void) 289 { 290 return false; 291 } 292 #endif 293 294 /* 295 * Checks if a buffer is all zeroes 296 */ 297 bool buffer_is_zero(const void *buf, size_t len) 298 { 299 if (unlikely(len == 0)) { 300 return true; 301 } 302 303 /* Fetch the beginning of the buffer while we select the accelerator. */ 304 __builtin_prefetch(buf); 305 306 /* Use an optimized zero check if possible. Note that this also 307 includes a check for an unrolled loop over 64-bit integers. */ 308 return select_accel_fn(buf, len); 309 } 310