/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright 2009 Sun Microsystems, Inc. All rights reserved. * Use is subject to license terms. */ /* * Fletcher Checksums * ------------------ * * ZFS's 2nd and 4th order Fletcher checksums are defined by the following * recurrence relations: * * a = a + f * i i-1 i-1 * * b = b + a * i i-1 i * * c = c + b (fletcher-4 only) * i i-1 i * * d = d + c (fletcher-4 only) * i i-1 i * * Where * a_0 = b_0 = c_0 = d_0 = 0 * and * f_0 .. f_(n-1) are the input data. * * Using standard techniques, these translate into the following series: * * __n_ __n_ * \ | \ | * a = > f b = > i * f * n /___| n - i n /___| n - i * i = 1 i = 1 * * * __n_ __n_ * \ | i*(i+1) \ | i*(i+1)*(i+2) * c = > ------- f d = > ------------- f * n /___| 2 n - i n /___| 6 n - i * i = 1 i = 1 * * For fletcher-2, the f_is are 64-bit, and [ab]_i are 64-bit accumulators. * Since the additions are done mod (2^64), errors in the high bits may not * be noticed. For this reason, fletcher-2 is deprecated. * * For fletcher-4, the f_is are 32-bit, and [abcd]_i are 64-bit accumulators. * A conservative estimate of how big the buffer can get before we overflow * can be estimated using f_i = 0xffffffff for all i: * * % bc * f=2^32-1;d=0; for (i = 1; d<2^64; i++) { d += f*i*(i+1)*(i+2)/6 }; (i-1)*4 * 2264 * quit * % * * So blocks of up to 2k will not overflow. Our largest block size is * 128k, which has 32k 4-byte words, so we can compute the largest possible * accumulators, then divide by 2^64 to figure the max amount of overflow: * * % bc * a=b=c=d=0; f=2^32-1; for (i=1; i<=32*1024; i++) { a+=f; b+=a; c+=b; d+=c } * a/2^64;b/2^64;c/2^64;d/2^64 * 0 * 0 * 1365 * 11186858 * quit * % * * So a and b cannot overflow. To make sure each bit of input has some * effect on the contents of c and d, we can look at what the factors of * the coefficients in the equations for c_n and d_n are. The number of 2s * in the factors determines the lowest set bit in the multiplier. Running * through the cases for n*(n+1)/2 reveals that the highest power of 2 is * 2^14, and for n*(n+1)*(n+2)/6 it is 2^15. So while some data may overflow * the 64-bit accumulators, every bit of every f_i effects every accumulator, * even for 128k blocks. * * If we wanted to make a stronger version of fletcher4 (fletcher4c?), * we could do our calculations mod (2^32 - 1) by adding in the carries * periodically, and store the number of carries in the top 32-bits. * * -------------------- * Checksum Performance * -------------------- * * There are two interesting components to checksum performance: cached and * uncached performance. With cached data, fletcher-2 is about four times * faster than fletcher-4. With uncached data, the performance difference is * negligible, since the cost of a cache fill dominates the processing time. * Even though fletcher-4 is slower than fletcher-2, it is still a pretty * efficient pass over the data. * * In normal operation, the data which is being checksummed is in a buffer * which has been filled either by: * * 1. a compression step, which will be mostly cached, or * 2. a bcopy() or copyin(), which will be uncached (because the * copy is cache-bypassing). * * For both cached and uncached data, both fletcher checksums are much faster * than sha-256, and slower than 'off', which doesn't touch the data at all. */ #include #include #include #include #include #include static void fletcher_4_scalar_init(zio_cksum_t *zcp); static void fletcher_4_scalar(const void *buf, uint64_t size, zio_cksum_t *zcp); static void fletcher_4_scalar_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp); static boolean_t fletcher_4_scalar_valid(void); static const fletcher_4_ops_t fletcher_4_scalar_ops = { .init = fletcher_4_scalar_init, .compute = fletcher_4_scalar, .compute_byteswap = fletcher_4_scalar_byteswap, .valid = fletcher_4_scalar_valid, .name = "scalar" }; static const fletcher_4_ops_t *fletcher_4_algos[] = { &fletcher_4_scalar_ops, #if defined(HAVE_AVX) && defined(HAVE_AVX2) &fletcher_4_avx2_ops, #endif }; static enum fletcher_selector { FLETCHER_FASTEST = 0, FLETCHER_SCALAR, #if defined(HAVE_AVX) && defined(HAVE_AVX2) FLETCHER_AVX2, #endif FLETCHER_CYCLE } fletcher_4_impl_chosen = FLETCHER_SCALAR; static struct fletcher_4_impl_selector { const char *fis_name; const fletcher_4_ops_t *fis_ops; } fletcher_4_impl_selectors[] = { [ FLETCHER_FASTEST ] = { "fastest", NULL }, [ FLETCHER_SCALAR ] = { "scalar", &fletcher_4_scalar_ops }, #if defined(HAVE_AVX) && defined(HAVE_AVX2) [ FLETCHER_AVX2 ] = { "avx2", &fletcher_4_avx2_ops }, #endif #if !defined(_KERNEL) [ FLETCHER_CYCLE ] = { "cycle", &fletcher_4_scalar_ops } #endif }; static kmutex_t fletcher_4_impl_lock; static kstat_t *fletcher_4_kstat; static kstat_named_t fletcher_4_kstat_data[ARRAY_SIZE(fletcher_4_algos)]; void fletcher_2_native(const void *buf, uint64_t size, zio_cksum_t *zcp) { const uint64_t *ip = buf; const uint64_t *ipend = ip + (size / sizeof (uint64_t)); uint64_t a0, b0, a1, b1; for (a0 = b0 = a1 = b1 = 0; ip < ipend; ip += 2) { a0 += ip[0]; a1 += ip[1]; b0 += a0; b1 += a1; } ZIO_SET_CHECKSUM(zcp, a0, a1, b0, b1); } void fletcher_2_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) { const uint64_t *ip = buf; const uint64_t *ipend = ip + (size / sizeof (uint64_t)); uint64_t a0, b0, a1, b1; for (a0 = b0 = a1 = b1 = 0; ip < ipend; ip += 2) { a0 += BSWAP_64(ip[0]); a1 += BSWAP_64(ip[1]); b0 += a0; b1 += a1; } ZIO_SET_CHECKSUM(zcp, a0, a1, b0, b1); } static void fletcher_4_scalar_init(zio_cksum_t *zcp) { ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0); } static void fletcher_4_scalar(const void *buf, uint64_t size, zio_cksum_t *zcp) { const uint32_t *ip = buf; const uint32_t *ipend = ip + (size / sizeof (uint32_t)); uint64_t a, b, c, d; a = zcp->zc_word[0]; b = zcp->zc_word[1]; c = zcp->zc_word[2]; d = zcp->zc_word[3]; for (; ip < ipend; ip++) { a += ip[0]; b += a; c += b; d += c; } ZIO_SET_CHECKSUM(zcp, a, b, c, d); } static void fletcher_4_scalar_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) { const uint32_t *ip = buf; const uint32_t *ipend = ip + (size / sizeof (uint32_t)); uint64_t a, b, c, d; a = zcp->zc_word[0]; b = zcp->zc_word[1]; c = zcp->zc_word[2]; d = zcp->zc_word[3]; for (; ip < ipend; ip++) { a += BSWAP_32(ip[0]); b += a; c += b; d += c; } ZIO_SET_CHECKSUM(zcp, a, b, c, d); } static boolean_t fletcher_4_scalar_valid(void) { return (B_TRUE); } int fletcher_4_impl_set(const char *val) { const fletcher_4_ops_t *ops; enum fletcher_selector idx; size_t val_len; unsigned i; val_len = strlen(val); while ((val_len > 0) && !!isspace(val[val_len-1])) /* trim '\n' */ val_len--; for (i = 0; i < ARRAY_SIZE(fletcher_4_impl_selectors); i++) { const char *name = fletcher_4_impl_selectors[i].fis_name; if (val_len == strlen(name) && strncmp(val, name, val_len) == 0) { idx = i; break; } } if (i >= ARRAY_SIZE(fletcher_4_impl_selectors)) return (-EINVAL); ops = fletcher_4_impl_selectors[idx].fis_ops; if (ops == NULL || !ops->valid()) return (-ENOTSUP); mutex_enter(&fletcher_4_impl_lock); if (fletcher_4_impl_chosen != idx) fletcher_4_impl_chosen = idx; mutex_exit(&fletcher_4_impl_lock); return (0); } static inline const fletcher_4_ops_t * fletcher_4_impl_get(void) { #if !defined(_KERNEL) if (fletcher_4_impl_chosen == FLETCHER_CYCLE) { static volatile unsigned int cycle_count = 0; const fletcher_4_ops_t *ops = NULL; unsigned int index; while (1) { index = atomic_inc_uint_nv(&cycle_count); ops = fletcher_4_algos[ index % ARRAY_SIZE(fletcher_4_algos)]; if (ops->valid()) break; } return (ops); } #endif membar_producer(); return (fletcher_4_impl_selectors[fletcher_4_impl_chosen].fis_ops); } void fletcher_4_native(const void *buf, uint64_t size, zio_cksum_t *zcp) { const fletcher_4_ops_t *ops; if (IS_P2ALIGNED(size, 4 * sizeof (uint32_t))) ops = fletcher_4_impl_get(); else ops = &fletcher_4_scalar_ops; ops->init(zcp); ops->compute(buf, size, zcp); if (ops->fini != NULL) ops->fini(zcp); } void fletcher_4_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) { const fletcher_4_ops_t *ops; if (IS_P2ALIGNED(size, 4 * sizeof (uint32_t))) ops = fletcher_4_impl_get(); else ops = &fletcher_4_scalar_ops; ops->init(zcp); ops->compute_byteswap(buf, size, zcp); if (ops->fini != NULL) ops->fini(zcp); } void fletcher_4_incremental_native(const void *buf, uint64_t size, zio_cksum_t *zcp) { fletcher_4_scalar(buf, size, zcp); } void fletcher_4_incremental_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) { fletcher_4_scalar_byteswap(buf, size, zcp); } void fletcher_4_init(void) { const uint64_t const bench_ns = (50 * MICROSEC); /* 50ms */ unsigned long best_run_count = 0; unsigned long best_run_index = 0; const unsigned data_size = 4096; char *databuf; int i; databuf = kmem_alloc(data_size, KM_SLEEP); for (i = 0; i < ARRAY_SIZE(fletcher_4_algos); i++) { const fletcher_4_ops_t *ops = fletcher_4_algos[i]; kstat_named_t *stat = &fletcher_4_kstat_data[i]; unsigned long run_count = 0; hrtime_t start; zio_cksum_t zc; strncpy(stat->name, ops->name, sizeof (stat->name) - 1); stat->data_type = KSTAT_DATA_UINT64; stat->value.ui64 = 0; if (!ops->valid()) continue; kpreempt_disable(); start = gethrtime(); ops->init(&zc); do { ops->compute(databuf, data_size, &zc); run_count++; } while (gethrtime() < start + bench_ns); if (ops->fini != NULL) ops->fini(&zc); kpreempt_enable(); if (run_count > best_run_count) { best_run_count = run_count; best_run_index = i; } /* * Due to high overhead of gethrtime(), the performance data * here is inaccurate and much slower than it could be. * It's fine for our use though because only relative speed * is important. */ stat->value.ui64 = data_size * run_count * (NANOSEC / bench_ns) >> 20; /* by MB/s */ } kmem_free(databuf, data_size); fletcher_4_impl_selectors[FLETCHER_FASTEST].fis_ops = fletcher_4_algos[best_run_index]; mutex_init(&fletcher_4_impl_lock, NULL, MUTEX_DEFAULT, NULL); fletcher_4_impl_set("fastest"); fletcher_4_kstat = kstat_create("zfs", 0, "fletcher_4_bench", "misc", KSTAT_TYPE_NAMED, ARRAY_SIZE(fletcher_4_algos), KSTAT_FLAG_VIRTUAL); if (fletcher_4_kstat != NULL) { fletcher_4_kstat->ks_data = fletcher_4_kstat_data; kstat_install(fletcher_4_kstat); } } void fletcher_4_fini(void) { mutex_destroy(&fletcher_4_impl_lock); if (fletcher_4_kstat != NULL) { kstat_delete(fletcher_4_kstat); fletcher_4_kstat = NULL; } } #if defined(_KERNEL) && defined(HAVE_SPL) static int fletcher_4_param_get(char *buffer, struct kernel_param *unused) { int i, cnt = 0; for (i = 0; i < ARRAY_SIZE(fletcher_4_impl_selectors); i++) { const fletcher_4_ops_t *ops; ops = fletcher_4_impl_selectors[i].fis_ops; if (!ops->valid()) continue; cnt += sprintf(buffer + cnt, fletcher_4_impl_chosen == i ? "[%s] " : "%s ", fletcher_4_impl_selectors[i].fis_name); } return (cnt); } static int fletcher_4_param_set(const char *val, struct kernel_param *unused) { return (fletcher_4_impl_set(val)); } /* * Choose a fletcher 4 implementation in ZFS. * Users can choose the "fastest" algorithm, or "scalar" and "avx2" which means * to compute fletcher 4 by CPU or vector instructions respectively. * Users can also choose "cycle" to exercise all implementions, but this is * for testing purpose therefore it can only be set in user space. */ module_param_call(zfs_fletcher_4_impl, fletcher_4_param_set, fletcher_4_param_get, NULL, 0644); MODULE_PARM_DESC(zfs_fletcher_4_impl, "Select fletcher 4 algorithm"); EXPORT_SYMBOL(fletcher_4_init); EXPORT_SYMBOL(fletcher_4_fini); EXPORT_SYMBOL(fletcher_2_native); EXPORT_SYMBOL(fletcher_2_byteswap); EXPORT_SYMBOL(fletcher_4_native); EXPORT_SYMBOL(fletcher_4_byteswap); EXPORT_SYMBOL(fletcher_4_incremental_native); EXPORT_SYMBOL(fletcher_4_incremental_byteswap); #endif