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34dc7c2f BB |
1 | /* |
2 | * CDDL HEADER START | |
3 | * | |
4 | * The contents of this file are subject to the terms of the | |
5 | * Common Development and Distribution License (the "License"). | |
6 | * You may not use this file except in compliance with the License. | |
7 | * | |
8 | * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE | |
9 | * or http://www.opensolaris.org/os/licensing. | |
10 | * See the License for the specific language governing permissions | |
11 | * and limitations under the License. | |
12 | * | |
13 | * When distributing Covered Code, include this CDDL HEADER in each | |
14 | * file and include the License file at usr/src/OPENSOLARIS.LICENSE. | |
15 | * If applicable, add the following below this CDDL HEADER, with the | |
16 | * fields enclosed by brackets "[]" replaced with your own identifying | |
17 | * information: Portions Copyright [yyyy] [name of copyright owner] | |
18 | * | |
19 | * CDDL HEADER END | |
20 | */ | |
21 | /* | |
9babb374 | 22 | * Copyright 2009 Sun Microsystems, Inc. All rights reserved. |
34dc7c2f BB |
23 | * Use is subject to license terms. |
24 | */ | |
25 | ||
9babb374 BB |
26 | /* |
27 | * Fletcher Checksums | |
28 | * ------------------ | |
29 | * | |
30 | * ZFS's 2nd and 4th order Fletcher checksums are defined by the following | |
31 | * recurrence relations: | |
32 | * | |
33 | * a = a + f | |
34 | * i i-1 i-1 | |
35 | * | |
36 | * b = b + a | |
37 | * i i-1 i | |
38 | * | |
39 | * c = c + b (fletcher-4 only) | |
40 | * i i-1 i | |
41 | * | |
42 | * d = d + c (fletcher-4 only) | |
43 | * i i-1 i | |
44 | * | |
45 | * Where | |
46 | * a_0 = b_0 = c_0 = d_0 = 0 | |
47 | * and | |
48 | * f_0 .. f_(n-1) are the input data. | |
49 | * | |
50 | * Using standard techniques, these translate into the following series: | |
51 | * | |
52 | * __n_ __n_ | |
53 | * \ | \ | | |
54 | * a = > f b = > i * f | |
55 | * n /___| n - i n /___| n - i | |
56 | * i = 1 i = 1 | |
57 | * | |
58 | * | |
59 | * __n_ __n_ | |
60 | * \ | i*(i+1) \ | i*(i+1)*(i+2) | |
61 | * c = > ------- f d = > ------------- f | |
62 | * n /___| 2 n - i n /___| 6 n - i | |
63 | * i = 1 i = 1 | |
64 | * | |
65 | * For fletcher-2, the f_is are 64-bit, and [ab]_i are 64-bit accumulators. | |
66 | * Since the additions are done mod (2^64), errors in the high bits may not | |
67 | * be noticed. For this reason, fletcher-2 is deprecated. | |
68 | * | |
69 | * For fletcher-4, the f_is are 32-bit, and [abcd]_i are 64-bit accumulators. | |
70 | * A conservative estimate of how big the buffer can get before we overflow | |
71 | * can be estimated using f_i = 0xffffffff for all i: | |
72 | * | |
73 | * % bc | |
74 | * f=2^32-1;d=0; for (i = 1; d<2^64; i++) { d += f*i*(i+1)*(i+2)/6 }; (i-1)*4 | |
75 | * 2264 | |
76 | * quit | |
77 | * % | |
78 | * | |
79 | * So blocks of up to 2k will not overflow. Our largest block size is | |
80 | * 128k, which has 32k 4-byte words, so we can compute the largest possible | |
81 | * accumulators, then divide by 2^64 to figure the max amount of overflow: | |
82 | * | |
83 | * % bc | |
84 | * a=b=c=d=0; f=2^32-1; for (i=1; i<=32*1024; i++) { a+=f; b+=a; c+=b; d+=c } | |
85 | * a/2^64;b/2^64;c/2^64;d/2^64 | |
86 | * 0 | |
87 | * 0 | |
88 | * 1365 | |
89 | * 11186858 | |
90 | * quit | |
91 | * % | |
92 | * | |
93 | * So a and b cannot overflow. To make sure each bit of input has some | |
94 | * effect on the contents of c and d, we can look at what the factors of | |
95 | * the coefficients in the equations for c_n and d_n are. The number of 2s | |
96 | * in the factors determines the lowest set bit in the multiplier. Running | |
97 | * through the cases for n*(n+1)/2 reveals that the highest power of 2 is | |
98 | * 2^14, and for n*(n+1)*(n+2)/6 it is 2^15. So while some data may overflow | |
99 | * the 64-bit accumulators, every bit of every f_i effects every accumulator, | |
100 | * even for 128k blocks. | |
101 | * | |
102 | * If we wanted to make a stronger version of fletcher4 (fletcher4c?), | |
103 | * we could do our calculations mod (2^32 - 1) by adding in the carries | |
104 | * periodically, and store the number of carries in the top 32-bits. | |
105 | * | |
106 | * -------------------- | |
107 | * Checksum Performance | |
108 | * -------------------- | |
109 | * | |
110 | * There are two interesting components to checksum performance: cached and | |
111 | * uncached performance. With cached data, fletcher-2 is about four times | |
112 | * faster than fletcher-4. With uncached data, the performance difference is | |
113 | * negligible, since the cost of a cache fill dominates the processing time. | |
114 | * Even though fletcher-4 is slower than fletcher-2, it is still a pretty | |
115 | * efficient pass over the data. | |
116 | * | |
117 | * In normal operation, the data which is being checksummed is in a buffer | |
118 | * which has been filled either by: | |
119 | * | |
120 | * 1. a compression step, which will be mostly cached, or | |
121 | * 2. a bcopy() or copyin(), which will be uncached (because the | |
122 | * copy is cache-bypassing). | |
123 | * | |
124 | * For both cached and uncached data, both fletcher checksums are much faster | |
125 | * than sha-256, and slower than 'off', which doesn't touch the data at all. | |
126 | */ | |
34dc7c2f BB |
127 | |
128 | #include <sys/types.h> | |
129 | #include <sys/sysmacros.h> | |
130 | #include <sys/byteorder.h> | |
131 | #include <sys/spa.h> | |
1eeb4562 JX |
132 | #include <sys/zfs_context.h> |
133 | #include <zfs_fletcher.h> | |
134 | ||
135 | static void fletcher_4_scalar_init(zio_cksum_t *zcp); | |
136 | static void fletcher_4_scalar(const void *buf, uint64_t size, | |
137 | zio_cksum_t *zcp); | |
138 | static void fletcher_4_scalar_byteswap(const void *buf, uint64_t size, | |
139 | zio_cksum_t *zcp); | |
140 | static boolean_t fletcher_4_scalar_valid(void); | |
141 | ||
142 | static const fletcher_4_ops_t fletcher_4_scalar_ops = { | |
143 | .init = fletcher_4_scalar_init, | |
144 | .compute = fletcher_4_scalar, | |
145 | .compute_byteswap = fletcher_4_scalar_byteswap, | |
146 | .valid = fletcher_4_scalar_valid, | |
147 | .name = "scalar" | |
148 | }; | |
149 | ||
150 | static const fletcher_4_ops_t *fletcher_4_algos[] = { | |
151 | &fletcher_4_scalar_ops, | |
152 | #if defined(HAVE_AVX) && defined(HAVE_AVX2) | |
153 | &fletcher_4_avx2_ops, | |
154 | #endif | |
155 | }; | |
156 | ||
157 | static enum fletcher_selector { | |
158 | FLETCHER_FASTEST = 0, | |
159 | FLETCHER_SCALAR, | |
160 | #if defined(HAVE_AVX) && defined(HAVE_AVX2) | |
161 | FLETCHER_AVX2, | |
162 | #endif | |
163 | FLETCHER_CYCLE | |
164 | } fletcher_4_impl_chosen = FLETCHER_SCALAR; | |
165 | ||
166 | static struct fletcher_4_impl_selector { | |
167 | const char *fis_name; | |
168 | const fletcher_4_ops_t *fis_ops; | |
169 | } fletcher_4_impl_selectors[] = { | |
170 | [ FLETCHER_FASTEST ] = { "fastest", NULL }, | |
171 | [ FLETCHER_SCALAR ] = { "scalar", &fletcher_4_scalar_ops }, | |
172 | #if defined(HAVE_AVX) && defined(HAVE_AVX2) | |
173 | [ FLETCHER_AVX2 ] = { "avx2", &fletcher_4_avx2_ops }, | |
174 | #endif | |
175 | #if !defined(_KERNEL) | |
176 | [ FLETCHER_CYCLE ] = { "cycle", &fletcher_4_scalar_ops } | |
177 | #endif | |
178 | }; | |
179 | ||
180 | static kmutex_t fletcher_4_impl_lock; | |
181 | ||
182 | static kstat_t *fletcher_4_kstat; | |
183 | ||
184 | static kstat_named_t fletcher_4_kstat_data[ARRAY_SIZE(fletcher_4_algos)]; | |
34dc7c2f BB |
185 | |
186 | void | |
187 | fletcher_2_native(const void *buf, uint64_t size, zio_cksum_t *zcp) | |
188 | { | |
189 | const uint64_t *ip = buf; | |
190 | const uint64_t *ipend = ip + (size / sizeof (uint64_t)); | |
191 | uint64_t a0, b0, a1, b1; | |
192 | ||
193 | for (a0 = b0 = a1 = b1 = 0; ip < ipend; ip += 2) { | |
194 | a0 += ip[0]; | |
195 | a1 += ip[1]; | |
196 | b0 += a0; | |
197 | b1 += a1; | |
198 | } | |
199 | ||
200 | ZIO_SET_CHECKSUM(zcp, a0, a1, b0, b1); | |
201 | } | |
202 | ||
203 | void | |
204 | fletcher_2_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) | |
205 | { | |
206 | const uint64_t *ip = buf; | |
207 | const uint64_t *ipend = ip + (size / sizeof (uint64_t)); | |
208 | uint64_t a0, b0, a1, b1; | |
209 | ||
210 | for (a0 = b0 = a1 = b1 = 0; ip < ipend; ip += 2) { | |
211 | a0 += BSWAP_64(ip[0]); | |
212 | a1 += BSWAP_64(ip[1]); | |
213 | b0 += a0; | |
214 | b1 += a1; | |
215 | } | |
216 | ||
217 | ZIO_SET_CHECKSUM(zcp, a0, a1, b0, b1); | |
218 | } | |
219 | ||
1eeb4562 | 220 | static void fletcher_4_scalar_init(zio_cksum_t *zcp) |
34dc7c2f | 221 | { |
1eeb4562 | 222 | ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0); |
34dc7c2f BB |
223 | } |
224 | ||
1eeb4562 JX |
225 | static void |
226 | fletcher_4_scalar(const void *buf, uint64_t size, zio_cksum_t *zcp) | |
34dc7c2f BB |
227 | { |
228 | const uint32_t *ip = buf; | |
229 | const uint32_t *ipend = ip + (size / sizeof (uint32_t)); | |
230 | uint64_t a, b, c, d; | |
231 | ||
1eeb4562 JX |
232 | a = zcp->zc_word[0]; |
233 | b = zcp->zc_word[1]; | |
234 | c = zcp->zc_word[2]; | |
235 | d = zcp->zc_word[3]; | |
236 | ||
237 | for (; ip < ipend; ip++) { | |
238 | a += ip[0]; | |
34dc7c2f BB |
239 | b += a; |
240 | c += b; | |
241 | d += c; | |
242 | } | |
243 | ||
244 | ZIO_SET_CHECKSUM(zcp, a, b, c, d); | |
245 | } | |
246 | ||
1eeb4562 JX |
247 | static void |
248 | fletcher_4_scalar_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) | |
34dc7c2f BB |
249 | { |
250 | const uint32_t *ip = buf; | |
251 | const uint32_t *ipend = ip + (size / sizeof (uint32_t)); | |
252 | uint64_t a, b, c, d; | |
253 | ||
254 | a = zcp->zc_word[0]; | |
255 | b = zcp->zc_word[1]; | |
256 | c = zcp->zc_word[2]; | |
257 | d = zcp->zc_word[3]; | |
258 | ||
259 | for (; ip < ipend; ip++) { | |
1eeb4562 | 260 | a += BSWAP_32(ip[0]); |
34dc7c2f BB |
261 | b += a; |
262 | c += b; | |
263 | d += c; | |
264 | } | |
265 | ||
266 | ZIO_SET_CHECKSUM(zcp, a, b, c, d); | |
267 | } | |
268 | ||
1eeb4562 JX |
269 | static boolean_t |
270 | fletcher_4_scalar_valid(void) | |
271 | { | |
272 | return (B_TRUE); | |
273 | } | |
274 | ||
275 | int | |
276 | fletcher_4_impl_set(const char *val) | |
277 | { | |
278 | const fletcher_4_ops_t *ops; | |
279 | enum fletcher_selector idx; | |
280 | size_t val_len; | |
281 | unsigned i; | |
282 | ||
283 | val_len = strlen(val); | |
284 | while ((val_len > 0) && !!isspace(val[val_len-1])) /* trim '\n' */ | |
285 | val_len--; | |
286 | ||
287 | for (i = 0; i < ARRAY_SIZE(fletcher_4_impl_selectors); i++) { | |
288 | const char *name = fletcher_4_impl_selectors[i].fis_name; | |
289 | ||
290 | if (val_len == strlen(name) && | |
291 | strncmp(val, name, val_len) == 0) { | |
292 | idx = i; | |
293 | break; | |
294 | } | |
295 | } | |
296 | if (i >= ARRAY_SIZE(fletcher_4_impl_selectors)) | |
297 | return (-EINVAL); | |
298 | ||
299 | ops = fletcher_4_impl_selectors[idx].fis_ops; | |
300 | if (ops == NULL || !ops->valid()) | |
301 | return (-ENOTSUP); | |
302 | ||
303 | mutex_enter(&fletcher_4_impl_lock); | |
304 | if (fletcher_4_impl_chosen != idx) | |
305 | fletcher_4_impl_chosen = idx; | |
306 | mutex_exit(&fletcher_4_impl_lock); | |
307 | ||
308 | return (0); | |
309 | } | |
310 | ||
311 | static inline const fletcher_4_ops_t * | |
312 | fletcher_4_impl_get(void) | |
313 | { | |
314 | #if !defined(_KERNEL) | |
315 | if (fletcher_4_impl_chosen == FLETCHER_CYCLE) { | |
316 | static volatile unsigned int cycle_count = 0; | |
317 | const fletcher_4_ops_t *ops = NULL; | |
318 | unsigned int index; | |
319 | ||
320 | while (1) { | |
321 | index = atomic_inc_uint_nv(&cycle_count); | |
322 | ops = fletcher_4_algos[ | |
323 | index % ARRAY_SIZE(fletcher_4_algos)]; | |
324 | if (ops->valid()) | |
325 | break; | |
326 | } | |
327 | return (ops); | |
328 | } | |
329 | #endif | |
330 | membar_producer(); | |
331 | return (fletcher_4_impl_selectors[fletcher_4_impl_chosen].fis_ops); | |
332 | } | |
333 | ||
334 | void | |
335 | fletcher_4_native(const void *buf, uint64_t size, zio_cksum_t *zcp) | |
336 | { | |
337 | const fletcher_4_ops_t *ops = fletcher_4_impl_get(); | |
338 | ||
339 | ops->init(zcp); | |
340 | ops->compute(buf, size, zcp); | |
341 | if (ops->fini != NULL) | |
342 | ops->fini(zcp); | |
343 | } | |
344 | ||
345 | void | |
346 | fletcher_4_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) | |
347 | { | |
348 | const fletcher_4_ops_t *ops = fletcher_4_impl_get(); | |
349 | ||
350 | ops->init(zcp); | |
351 | ops->compute_byteswap(buf, size, zcp); | |
352 | if (ops->fini != NULL) | |
353 | ops->fini(zcp); | |
354 | } | |
355 | ||
356 | void | |
357 | fletcher_4_incremental_native(const void *buf, uint64_t size, | |
358 | zio_cksum_t *zcp) | |
359 | { | |
360 | fletcher_4_scalar(buf, size, zcp); | |
361 | } | |
362 | ||
34dc7c2f BB |
363 | void |
364 | fletcher_4_incremental_byteswap(const void *buf, uint64_t size, | |
365 | zio_cksum_t *zcp) | |
366 | { | |
1eeb4562 JX |
367 | fletcher_4_scalar_byteswap(buf, size, zcp); |
368 | } | |
34dc7c2f | 369 | |
1eeb4562 JX |
370 | void |
371 | fletcher_4_init(void) | |
372 | { | |
373 | const uint64_t const bench_ns = (50 * MICROSEC); /* 50ms */ | |
374 | unsigned long best_run_count = 0; | |
375 | unsigned long best_run_index = 0; | |
376 | const unsigned data_size = 4096; | |
377 | char *databuf; | |
378 | int i; | |
34dc7c2f | 379 | |
1eeb4562 JX |
380 | databuf = kmem_alloc(data_size, KM_SLEEP); |
381 | for (i = 0; i < ARRAY_SIZE(fletcher_4_algos); i++) { | |
382 | const fletcher_4_ops_t *ops = fletcher_4_algos[i]; | |
383 | kstat_named_t *stat = &fletcher_4_kstat_data[i]; | |
384 | unsigned long run_count = 0; | |
385 | hrtime_t start; | |
386 | zio_cksum_t zc; | |
387 | ||
388 | strncpy(stat->name, ops->name, sizeof (stat->name) - 1); | |
389 | stat->data_type = KSTAT_DATA_UINT64; | |
390 | stat->value.ui64 = 0; | |
391 | ||
392 | if (!ops->valid()) | |
393 | continue; | |
394 | ||
395 | kpreempt_disable(); | |
396 | start = gethrtime(); | |
397 | ops->init(&zc); | |
398 | do { | |
399 | ops->compute(databuf, data_size, &zc); | |
400 | run_count++; | |
401 | } while (gethrtime() < start + bench_ns); | |
402 | if (ops->fini != NULL) | |
403 | ops->fini(&zc); | |
404 | kpreempt_enable(); | |
405 | ||
406 | if (run_count > best_run_count) { | |
407 | best_run_count = run_count; | |
408 | best_run_index = i; | |
409 | } | |
410 | ||
411 | /* | |
412 | * Due to high overhead of gethrtime(), the performance data | |
413 | * here is inaccurate and much slower than it could be. | |
414 | * It's fine for our use though because only relative speed | |
415 | * is important. | |
416 | */ | |
417 | stat->value.ui64 = data_size * run_count * | |
418 | (NANOSEC / bench_ns) >> 20; /* by MB/s */ | |
34dc7c2f | 419 | } |
1eeb4562 | 420 | kmem_free(databuf, data_size); |
34dc7c2f | 421 | |
1eeb4562 JX |
422 | fletcher_4_impl_selectors[FLETCHER_FASTEST].fis_ops = |
423 | fletcher_4_algos[best_run_index]; | |
424 | ||
425 | mutex_init(&fletcher_4_impl_lock, NULL, MUTEX_DEFAULT, NULL); | |
426 | fletcher_4_impl_set("fastest"); | |
427 | ||
428 | fletcher_4_kstat = kstat_create("zfs", 0, "fletcher_4_bench", | |
429 | "misc", KSTAT_TYPE_NAMED, ARRAY_SIZE(fletcher_4_algos), | |
430 | KSTAT_FLAG_VIRTUAL); | |
431 | if (fletcher_4_kstat != NULL) { | |
432 | fletcher_4_kstat->ks_data = fletcher_4_kstat_data; | |
433 | kstat_install(fletcher_4_kstat); | |
434 | } | |
435 | } | |
436 | ||
437 | void | |
438 | fletcher_4_fini(void) | |
439 | { | |
440 | mutex_destroy(&fletcher_4_impl_lock); | |
441 | if (fletcher_4_kstat != NULL) { | |
442 | kstat_delete(fletcher_4_kstat); | |
443 | fletcher_4_kstat = NULL; | |
444 | } | |
34dc7c2f | 445 | } |
c28b2279 BB |
446 | |
447 | #if defined(_KERNEL) && defined(HAVE_SPL) | |
1eeb4562 JX |
448 | |
449 | static int | |
450 | fletcher_4_param_get(char *buffer, struct kernel_param *unused) | |
451 | { | |
452 | int i, cnt = 0; | |
453 | ||
454 | for (i = 0; i < ARRAY_SIZE(fletcher_4_impl_selectors); i++) { | |
455 | const fletcher_4_ops_t *ops; | |
456 | ||
457 | ops = fletcher_4_impl_selectors[i].fis_ops; | |
458 | if (!ops->valid()) | |
459 | continue; | |
460 | ||
461 | cnt += sprintf(buffer + cnt, | |
462 | fletcher_4_impl_chosen == i ? "[%s] " : "%s ", | |
463 | fletcher_4_impl_selectors[i].fis_name); | |
464 | } | |
465 | ||
466 | return (cnt); | |
467 | } | |
468 | ||
469 | static int | |
470 | fletcher_4_param_set(const char *val, struct kernel_param *unused) | |
471 | { | |
472 | return (fletcher_4_impl_set(val)); | |
473 | } | |
474 | ||
475 | /* | |
476 | * Choose a fletcher 4 implementation in ZFS. | |
477 | * Users can choose the "fastest" algorithm, or "scalar" and "avx2" which means | |
478 | * to compute fletcher 4 by CPU or vector instructions respectively. | |
479 | * Users can also choose "cycle" to exercise all implementions, but this is | |
480 | * for testing purpose therefore it can only be set in user space. | |
481 | */ | |
482 | module_param_call(zfs_fletcher_4_impl, | |
483 | fletcher_4_param_set, fletcher_4_param_get, NULL, 0644); | |
484 | MODULE_PARM_DESC(zfs_fletcher_4_impl, "Select fletcher 4 algorithm"); | |
485 | ||
486 | EXPORT_SYMBOL(fletcher_4_init); | |
487 | EXPORT_SYMBOL(fletcher_4_fini); | |
c28b2279 BB |
488 | EXPORT_SYMBOL(fletcher_2_native); |
489 | EXPORT_SYMBOL(fletcher_2_byteswap); | |
490 | EXPORT_SYMBOL(fletcher_4_native); | |
491 | EXPORT_SYMBOL(fletcher_4_byteswap); | |
492 | EXPORT_SYMBOL(fletcher_4_incremental_native); | |
493 | EXPORT_SYMBOL(fletcher_4_incremental_byteswap); | |
494 | #endif |