memory: add support getting and using a dirty bitmap copy.
[qemu.git] / util / bufferiszero.c
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-common.h"
26 #include "qemu/cutils.h"
27 #include "qemu/bswap.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_AVX2_OPT) || defined(__SSE2__)
68 /* Do not use push_options pragmas unnecessarily, because clang
69 * does not support them.
70 */
71 #ifdef CONFIG_AVX2_OPT
72 #pragma GCC push_options
73 #pragma GCC target("sse2")
74 #endif
75 #include <emmintrin.h>
76
77 /* Note that each of these vectorized functions require len >= 64. */
78
79 static bool
80 buffer_zero_sse2(const void *buf, size_t len)
81 {
82 __m128i t = _mm_loadu_si128(buf);
83 __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16);
84 __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16);
85 __m128i zero = _mm_setzero_si128();
86
87 /* Loop over 16-byte aligned blocks of 64. */
88 while (likely(p <= e)) {
89 __builtin_prefetch(p);
90 t = _mm_cmpeq_epi8(t, zero);
91 if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) {
92 return false;
93 }
94 t = p[-4] | p[-3] | p[-2] | p[-1];
95 p += 4;
96 }
97
98 /* Finish the aligned tail. */
99 t |= e[-3];
100 t |= e[-2];
101 t |= e[-1];
102
103 /* Finish the unaligned tail. */
104 t |= _mm_loadu_si128(buf + len - 16);
105
106 return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF;
107 }
108 #ifdef CONFIG_AVX2_OPT
109 #pragma GCC pop_options
110 #endif
111
112 #ifdef CONFIG_AVX2_OPT
113 /* Note that due to restrictions/bugs wrt __builtin functions in gcc <= 4.8,
114 * the includes have to be within the corresponding push_options region, and
115 * therefore the regions themselves have to be ordered with increasing ISA.
116 */
117 #pragma GCC push_options
118 #pragma GCC target("sse4")
119 #include <smmintrin.h>
120
121 static bool
122 buffer_zero_sse4(const void *buf, size_t len)
123 {
124 __m128i t = _mm_loadu_si128(buf);
125 __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16);
126 __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16);
127
128 /* Loop over 16-byte aligned blocks of 64. */
129 while (likely(p <= e)) {
130 __builtin_prefetch(p);
131 if (unlikely(!_mm_testz_si128(t, t))) {
132 return false;
133 }
134 t = p[-4] | p[-3] | p[-2] | p[-1];
135 p += 4;
136 }
137
138 /* Finish the aligned tail. */
139 t |= e[-3];
140 t |= e[-2];
141 t |= e[-1];
142
143 /* Finish the unaligned tail. */
144 t |= _mm_loadu_si128(buf + len - 16);
145
146 return _mm_testz_si128(t, t);
147 }
148
149 #pragma GCC pop_options
150 #pragma GCC push_options
151 #pragma GCC target("avx2")
152 #include <immintrin.h>
153
154 static bool
155 buffer_zero_avx2(const void *buf, size_t len)
156 {
157 /* Begin with an unaligned head of 32 bytes. */
158 __m256i t = _mm256_loadu_si256(buf);
159 __m256i *p = (__m256i *)(((uintptr_t)buf + 5 * 32) & -32);
160 __m256i *e = (__m256i *)(((uintptr_t)buf + len) & -32);
161
162 if (likely(p <= e)) {
163 /* Loop over 32-byte aligned blocks of 128. */
164 do {
165 __builtin_prefetch(p);
166 if (unlikely(!_mm256_testz_si256(t, t))) {
167 return false;
168 }
169 t = p[-4] | p[-3] | p[-2] | p[-1];
170 p += 4;
171 } while (p <= e);
172 } else {
173 t |= _mm256_loadu_si256(buf + 32);
174 if (len <= 128) {
175 goto last2;
176 }
177 }
178
179 /* Finish the last block of 128 unaligned. */
180 t |= _mm256_loadu_si256(buf + len - 4 * 32);
181 t |= _mm256_loadu_si256(buf + len - 3 * 32);
182 last2:
183 t |= _mm256_loadu_si256(buf + len - 2 * 32);
184 t |= _mm256_loadu_si256(buf + len - 1 * 32);
185
186 return _mm256_testz_si256(t, t);
187 }
188 #pragma GCC pop_options
189 #endif /* CONFIG_AVX2_OPT */
190
191 /* Note that for test_buffer_is_zero_next_accel, the most preferred
192 * ISA must have the least significant bit.
193 */
194 #define CACHE_AVX2 1
195 #define CACHE_SSE4 2
196 #define CACHE_SSE2 4
197
198 /* Make sure that these variables are appropriately initialized when
199 * SSE2 is enabled on the compiler command-line, but the compiler is
200 * too old to support <cpuid.h>.
201 */
202 #ifdef CONFIG_AVX2_OPT
203 # define INIT_CACHE 0
204 # define INIT_ACCEL buffer_zero_int
205 #else
206 # ifndef __SSE2__
207 # error "ISA selection confusion"
208 # endif
209 # define INIT_CACHE CACHE_SSE2
210 # define INIT_ACCEL buffer_zero_sse2
211 #endif
212
213 static unsigned cpuid_cache = INIT_CACHE;
214 static bool (*buffer_accel)(const void *, size_t) = INIT_ACCEL;
215
216 static void init_accel(unsigned cache)
217 {
218 bool (*fn)(const void *, size_t) = buffer_zero_int;
219 if (cache & CACHE_SSE2) {
220 fn = buffer_zero_sse2;
221 }
222 #ifdef CONFIG_AVX2_OPT
223 if (cache & CACHE_SSE4) {
224 fn = buffer_zero_sse4;
225 }
226 if (cache & CACHE_AVX2) {
227 fn = buffer_zero_avx2;
228 }
229 #endif
230 buffer_accel = fn;
231 }
232
233 #ifdef CONFIG_AVX2_OPT
234 #include <cpuid.h>
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 #ifdef CONFIG_AVX2_OPT
247 if (c & bit_SSE4_1) {
248 cache |= CACHE_SSE4;
249 }
250
251 /* We must check that AVX is not just available, but usable. */
252 if ((c & bit_OSXSAVE) && (c & bit_AVX) && max >= 7) {
253 int bv;
254 __asm("xgetbv" : "=a"(bv), "=d"(d) : "c"(0));
255 __cpuid_count(7, 0, a, b, c, d);
256 if ((bv & 6) == 6 && (b & bit_AVX2)) {
257 cache |= CACHE_AVX2;
258 }
259 }
260 #endif
261 }
262 cpuid_cache = cache;
263 init_accel(cache);
264 }
265 #endif /* CONFIG_AVX2_OPT */
266
267 bool test_buffer_is_zero_next_accel(void)
268 {
269 /* If no bits set, we just tested buffer_zero_int, and there
270 are no more acceleration options to test. */
271 if (cpuid_cache == 0) {
272 return false;
273 }
274 /* Disable the accelerator we used before and select a new one. */
275 cpuid_cache &= cpuid_cache - 1;
276 init_accel(cpuid_cache);
277 return true;
278 }
279
280 static bool select_accel_fn(const void *buf, size_t len)
281 {
282 if (likely(len >= 64)) {
283 return buffer_accel(buf, len);
284 }
285 return buffer_zero_int(buf, len);
286 }
287
288 #else
289 #define select_accel_fn buffer_zero_int
290 bool test_buffer_is_zero_next_accel(void)
291 {
292 return false;
293 }
294 #endif
295
296 /*
297 * Checks if a buffer is all zeroes
298 */
299 bool buffer_is_zero(const void *buf, size_t len)
300 {
301 if (unlikely(len == 0)) {
302 return true;
303 }
304
305 /* Fetch the beginning of the buffer while we select the accelerator. */
306 __builtin_prefetch(buf);
307
308 /* Use an optimized zero check if possible. Note that this also
309 includes a check for an unrolled loop over 64-bit integers. */
310 return select_accel_fn(buf, len);
311 }