DLPX-44812 integrate EP-220 large memory scalability

[mirror_zfs.git] / module / zcommon / zfs_fletcher.c

/*
 * 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.
 * Copyright (C) 2016 Gvozden Nešković. All rights reserved.
 */
/*
 * Copyright 2013 Saso Kiselkov. All rights reserved.
 */

/*
 * Copyright (c) 2016 by Delphix. All rights reserved.
 */

/*
 * 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 <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/byteorder.h>
#include <sys/spa.h>
#include <sys/zio_checksum.h>
#include <sys/zfs_context.h>
#include <zfs_fletcher.h>


static void fletcher_4_scalar_init(fletcher_4_ctx_t *ctx);
static void fletcher_4_scalar_fini(fletcher_4_ctx_t *ctx, zio_cksum_t *zcp);
static void fletcher_4_scalar_native(fletcher_4_ctx_t *ctx,
    const void *buf, uint64_t size);
static void fletcher_4_scalar_byteswap(fletcher_4_ctx_t *ctx,
    const void *buf, uint64_t size);
static boolean_t fletcher_4_scalar_valid(void);

static const fletcher_4_ops_t fletcher_4_scalar_ops = {
        .init_native = fletcher_4_scalar_init,
        .fini_native = fletcher_4_scalar_fini,
        .compute_native = fletcher_4_scalar_native,
        .init_byteswap = fletcher_4_scalar_init,
        .fini_byteswap = fletcher_4_scalar_fini,
        .compute_byteswap = fletcher_4_scalar_byteswap,
        .valid = fletcher_4_scalar_valid,
        .name = "scalar"
};

static fletcher_4_ops_t fletcher_4_fastest_impl = {
        .name = "fastest",
        .valid = fletcher_4_scalar_valid
};

static const fletcher_4_ops_t *fletcher_4_impls[] = {
        &fletcher_4_scalar_ops,
        &fletcher_4_superscalar_ops,
        &fletcher_4_superscalar4_ops,
#if defined(HAVE_SSE2)
        &fletcher_4_sse2_ops,
#endif
#if defined(HAVE_SSE2) && defined(HAVE_SSSE3)
        &fletcher_4_ssse3_ops,
#endif
#if defined(HAVE_AVX) && defined(HAVE_AVX2)
        &fletcher_4_avx2_ops,
#endif
#if defined(__x86_64) && defined(HAVE_AVX512F)
        &fletcher_4_avx512f_ops,
#endif
#if defined(__aarch64__)
        &fletcher_4_aarch64_neon_ops,
#endif
};

/* Hold all supported implementations */
static uint32_t fletcher_4_supp_impls_cnt = 0;
static fletcher_4_ops_t *fletcher_4_supp_impls[ARRAY_SIZE(fletcher_4_impls)];

/* Select fletcher4 implementation */
#define IMPL_FASTEST    (UINT32_MAX)
#define IMPL_CYCLE      (UINT32_MAX - 1)
#define IMPL_SCALAR     (0)

static uint32_t fletcher_4_impl_chosen = IMPL_FASTEST;

#define IMPL_READ(i)    (*(volatile uint32_t *) &(i))

static struct fletcher_4_impl_selector {
        const char      *fis_name;
        uint32_t        fis_sel;
} fletcher_4_impl_selectors[] = {
#if !defined(_KERNEL)
        { "cycle",      IMPL_CYCLE },
#endif
        { "fastest",    IMPL_FASTEST },
        { "scalar",     IMPL_SCALAR }
};

static kstat_t *fletcher_4_kstat;

static struct fletcher_4_kstat {
        uint64_t native;
        uint64_t byteswap;
} fletcher_4_stat_data[ARRAY_SIZE(fletcher_4_impls) + 1];

/* Indicate that benchmark has been completed */
static boolean_t fletcher_4_initialized = B_FALSE;

/*ARGSUSED*/
void
fletcher_init(zio_cksum_t *zcp)
{
        ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0);
}

int
fletcher_2_incremental_native(void *buf, size_t size, void *data)
{
        zio_cksum_t *zcp = data;

        const uint64_t *ip = buf;
        const uint64_t *ipend = ip + (size / sizeof (uint64_t));
        uint64_t a0, b0, a1, b1;

        a0 = zcp->zc_word[0];
        a1 = zcp->zc_word[1];
        b0 = zcp->zc_word[2];
        b1 = zcp->zc_word[3];

        for (; ip < ipend; ip += 2) {
                a0 += ip[0];
                a1 += ip[1];
                b0 += a0;
                b1 += a1;
        }

        ZIO_SET_CHECKSUM(zcp, a0, a1, b0, b1);
        return (0);
}

/*ARGSUSED*/
void
fletcher_2_native(const void *buf, uint64_t size,
    const void *ctx_template, zio_cksum_t *zcp)
{
        fletcher_init(zcp);
        (void) fletcher_2_incremental_native((void *) buf, size, zcp);
}

int
fletcher_2_incremental_byteswap(void *buf, size_t size, void *data)
{
        zio_cksum_t *zcp = data;

        const uint64_t *ip = buf;
        const uint64_t *ipend = ip + (size / sizeof (uint64_t));
        uint64_t a0, b0, a1, b1;

        a0 = zcp->zc_word[0];
        a1 = zcp->zc_word[1];
        b0 = zcp->zc_word[2];
        b1 = zcp->zc_word[3];

        for (; 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);
        return (0);
}

/*ARGSUSED*/
void
fletcher_2_byteswap(const void *buf, uint64_t size,
    const void *ctx_template, zio_cksum_t *zcp)
{
        fletcher_init(zcp);
        (void) fletcher_2_incremental_byteswap((void *) buf, size, zcp);
}

static void
fletcher_4_scalar_init(fletcher_4_ctx_t *ctx)
{
        ZIO_SET_CHECKSUM(&ctx->scalar, 0, 0, 0, 0);
}

static void
fletcher_4_scalar_fini(fletcher_4_ctx_t *ctx, zio_cksum_t *zcp)
{
        memcpy(zcp, &ctx->scalar, sizeof (zio_cksum_t));
}

static void
fletcher_4_scalar_native(fletcher_4_ctx_t *ctx, const void *buf,
    uint64_t size)
{
        const uint32_t *ip = buf;
        const uint32_t *ipend = ip + (size / sizeof (uint32_t));
        uint64_t a, b, c, d;

        a = ctx->scalar.zc_word[0];
        b = ctx->scalar.zc_word[1];
        c = ctx->scalar.zc_word[2];
        d = ctx->scalar.zc_word[3];

        for (; ip < ipend; ip++) {
                a += ip[0];
                b += a;
                c += b;
                d += c;
        }

        ZIO_SET_CHECKSUM(&ctx->scalar, a, b, c, d);
}

static void
fletcher_4_scalar_byteswap(fletcher_4_ctx_t *ctx, const void *buf,
    uint64_t size)
{
        const uint32_t *ip = buf;
        const uint32_t *ipend = ip + (size / sizeof (uint32_t));
        uint64_t a, b, c, d;

        a = ctx->scalar.zc_word[0];
        b = ctx->scalar.zc_word[1];
        c = ctx->scalar.zc_word[2];
        d = ctx->scalar.zc_word[3];

        for (; ip < ipend; ip++) {
                a += BSWAP_32(ip[0]);
                b += a;
                c += b;
                d += c;
        }

        ZIO_SET_CHECKSUM(&ctx->scalar, a, b, c, d);
}

static boolean_t
fletcher_4_scalar_valid(void)
{
        return (B_TRUE);
}

int
fletcher_4_impl_set(const char *val)
{
        int err = -EINVAL;
        uint32_t impl = IMPL_READ(fletcher_4_impl_chosen);
        size_t i, val_len;

        val_len = strlen(val);
        while ((val_len > 0) && !!isspace(val[val_len-1])) /* trim '\n' */
                val_len--;

        /* check mandatory implementations */
        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) {
                        impl = fletcher_4_impl_selectors[i].fis_sel;
                        err = 0;
                        break;
                }
        }

        if (err != 0 && fletcher_4_initialized) {
                /* check all supported implementations */
                for (i = 0; i < fletcher_4_supp_impls_cnt; i++) {
                        const char *name = fletcher_4_supp_impls[i]->name;

                        if (val_len == strlen(name) &&
                            strncmp(val, name, val_len) == 0) {
                                impl = i;
                                err = 0;
                                break;
                        }
                }
        }

        if (err == 0) {
                atomic_swap_32(&fletcher_4_impl_chosen, impl);
                membar_producer();
        }

        return (err);
}

static inline const fletcher_4_ops_t *
fletcher_4_impl_get(void)
{
        fletcher_4_ops_t *ops = NULL;
        const uint32_t impl = IMPL_READ(fletcher_4_impl_chosen);

        switch (impl) {
        case IMPL_FASTEST:
                ASSERT(fletcher_4_initialized);
                ops = &fletcher_4_fastest_impl;
                break;
#if !defined(_KERNEL)
        case IMPL_CYCLE: {
                ASSERT(fletcher_4_initialized);
                ASSERT3U(fletcher_4_supp_impls_cnt, >, 0);

                static uint32_t cycle_count = 0;
                uint32_t idx = (++cycle_count) % fletcher_4_supp_impls_cnt;
                ops = fletcher_4_supp_impls[idx];
        }
        break;
#endif
        default:
                ASSERT3U(fletcher_4_supp_impls_cnt, >, 0);
                ASSERT3U(impl, <, fletcher_4_supp_impls_cnt);

                ops = fletcher_4_supp_impls[impl];
                break;
        }

        ASSERT3P(ops, !=, NULL);

        return (ops);
}

static inline void
fletcher_4_native_impl(const void *buf, uint64_t size, zio_cksum_t *zcp)
{
        fletcher_4_ctx_t ctx;
        const fletcher_4_ops_t *ops = fletcher_4_impl_get();

        ops->init_native(&ctx);
        ops->compute_native(&ctx, buf, size);
        ops->fini_native(&ctx, zcp);
}

/*ARGSUSED*/
void
fletcher_4_native(const void *buf, uint64_t size,
    const void *ctx_template, zio_cksum_t *zcp)
{
        const uint64_t p2size = P2ALIGN(size, 64);

        ASSERT(IS_P2ALIGNED(size, sizeof (uint32_t)));

        if (size == 0 || p2size == 0) {
                ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0);

                if (size > 0)
                        fletcher_4_scalar_native((fletcher_4_ctx_t *)zcp,
                            buf, size);
        } else {
                fletcher_4_native_impl(buf, p2size, zcp);

                if (p2size < size)
                        fletcher_4_scalar_native((fletcher_4_ctx_t *)zcp,
                            (char *)buf + p2size, size - p2size);
        }
}

void
fletcher_4_native_varsize(const void *buf, uint64_t size, zio_cksum_t *zcp)
{
        ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0);
        fletcher_4_scalar_native((fletcher_4_ctx_t *)zcp, buf, size);
}

static inline void
fletcher_4_byteswap_impl(const void *buf, uint64_t size, zio_cksum_t *zcp)
{
        fletcher_4_ctx_t ctx;
        const fletcher_4_ops_t *ops = fletcher_4_impl_get();

        ops->init_byteswap(&ctx);
        ops->compute_byteswap(&ctx, buf, size);
        ops->fini_byteswap(&ctx, zcp);
}

/*ARGSUSED*/
void
fletcher_4_byteswap(const void *buf, uint64_t size,
    const void *ctx_template, zio_cksum_t *zcp)
{
        const uint64_t p2size = P2ALIGN(size, 64);

        ASSERT(IS_P2ALIGNED(size, sizeof (uint32_t)));

        if (size == 0 || p2size == 0) {
                ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0);

                if (size > 0)
                        fletcher_4_scalar_byteswap((fletcher_4_ctx_t *)zcp,
                            buf, size);
        } else {
                fletcher_4_byteswap_impl(buf, p2size, zcp);

                if (p2size < size)
                        fletcher_4_scalar_byteswap((fletcher_4_ctx_t *)zcp,
                            (char *)buf + p2size, size - p2size);
        }
}

/* Incremental Fletcher 4 */

#define ZFS_FLETCHER_4_INC_MAX_SIZE     (8ULL << 20)

static inline void
fletcher_4_incremental_combine(zio_cksum_t *zcp, const uint64_t size,
    const zio_cksum_t *nzcp)
{
        const uint64_t c1 = size / sizeof (uint32_t);
        const uint64_t c2 = c1 * (c1 + 1) / 2;
        const uint64_t c3 = c2 * (c1 + 2) / 3;

        /*
         * Value of 'c3' overflows on buffer sizes close to 16MiB. For that
         * reason we split incremental fletcher4 computation of large buffers
         * to steps of (ZFS_FLETCHER_4_INC_MAX_SIZE) size.
         */
        ASSERT3U(size, <=, ZFS_FLETCHER_4_INC_MAX_SIZE);

        zcp->zc_word[3] += nzcp->zc_word[3] + c1 * zcp->zc_word[2] +
            c2 * zcp->zc_word[1] + c3 * zcp->zc_word[0];
        zcp->zc_word[2] += nzcp->zc_word[2] + c1 * zcp->zc_word[1] +
            c2 * zcp->zc_word[0];
        zcp->zc_word[1] += nzcp->zc_word[1] + c1 * zcp->zc_word[0];
        zcp->zc_word[0] += nzcp->zc_word[0];
}

static inline void
fletcher_4_incremental_impl(boolean_t native, const void *buf, uint64_t size,
    zio_cksum_t *zcp)
{
        while (size > 0) {
                zio_cksum_t nzc;
                uint64_t len = MIN(size, ZFS_FLETCHER_4_INC_MAX_SIZE);

                if (native)
                        fletcher_4_native(buf, len, NULL, &nzc);
                else
                        fletcher_4_byteswap(buf, len, NULL, &nzc);

                fletcher_4_incremental_combine(zcp, len, &nzc);

                size -= len;
                buf += len;
        }
}

int
fletcher_4_incremental_native(void *buf, size_t size, void *data)
{
        zio_cksum_t *zcp = data;
        /* Use scalar impl to directly update cksum of small blocks */
        if (size < SPA_MINBLOCKSIZE)
                fletcher_4_scalar_native((fletcher_4_ctx_t *)zcp, buf, size);
        else
                fletcher_4_incremental_impl(B_TRUE, buf, size, zcp);
        return (0);
}

int
fletcher_4_incremental_byteswap(void *buf, size_t size, void *data)
{
        zio_cksum_t *zcp = data;
        /* Use scalar impl to directly update cksum of small blocks */
        if (size < SPA_MINBLOCKSIZE)
                fletcher_4_scalar_byteswap((fletcher_4_ctx_t *)zcp, buf, size);
        else
                fletcher_4_incremental_impl(B_FALSE, buf, size, zcp);
        return (0);
}


/* Fletcher 4 kstats */

static int
fletcher_4_kstat_headers(char *buf, size_t size)
{
        ssize_t off = 0;

        off += snprintf(buf + off, size, "%-17s", "implementation");
        off += snprintf(buf + off, size - off, "%-15s", "native");
        (void) snprintf(buf + off, size - off, "%-15s\n", "byteswap");

        return (0);
}

static int
fletcher_4_kstat_data(char *buf, size_t size, void *data)
{
        struct fletcher_4_kstat *fastest_stat =
            &fletcher_4_stat_data[fletcher_4_supp_impls_cnt];
        struct fletcher_4_kstat *curr_stat = (struct fletcher_4_kstat *) data;
        ssize_t off = 0;

        if (curr_stat == fastest_stat) {
                off += snprintf(buf + off, size - off, "%-17s", "fastest");
                off += snprintf(buf + off, size - off, "%-15s",
                    fletcher_4_supp_impls[fastest_stat->native]->name);
                off += snprintf(buf + off, size - off, "%-15s\n",
                    fletcher_4_supp_impls[fastest_stat->byteswap]->name);
        } else {
                ptrdiff_t id = curr_stat - fletcher_4_stat_data;

                off += snprintf(buf + off, size - off, "%-17s",
                    fletcher_4_supp_impls[id]->name);
                off += snprintf(buf + off, size - off, "%-15llu",
                            (u_longlong_t) curr_stat->native);
                off += snprintf(buf + off, size - off, "%-15llu\n",
                            (u_longlong_t) curr_stat->byteswap);
        }

        return (0);
}

static void *
fletcher_4_kstat_addr(kstat_t *ksp, loff_t n)
{
        if (n <= fletcher_4_supp_impls_cnt)
                ksp->ks_private = (void *) (fletcher_4_stat_data + n);
        else
                ksp->ks_private = NULL;

        return (ksp->ks_private);
}

#define FLETCHER_4_FASTEST_FN_COPY(type, src)                             \
{                                                                         \
        fletcher_4_fastest_impl.init_ ## type = src->init_ ## type;       \
        fletcher_4_fastest_impl.fini_ ## type = src->fini_ ## type;       \
        fletcher_4_fastest_impl.compute_ ## type = src->compute_ ## type; \
}

#define FLETCHER_4_BENCH_NS     (MSEC2NSEC(50))         /* 50ms */

typedef void fletcher_checksum_func_t(const void *, uint64_t, const void *,
                                        zio_cksum_t *);

static void
fletcher_4_benchmark_impl(boolean_t native, char *data, uint64_t data_size)
{

        struct fletcher_4_kstat *fastest_stat =
            &fletcher_4_stat_data[fletcher_4_supp_impls_cnt];
        hrtime_t start;
        uint64_t run_bw, run_time_ns, best_run = 0;
        zio_cksum_t zc;
        uint32_t i, l, sel_save = IMPL_READ(fletcher_4_impl_chosen);


        fletcher_checksum_func_t *fletcher_4_test = native ?
            fletcher_4_native : fletcher_4_byteswap;

        for (i = 0; i < fletcher_4_supp_impls_cnt; i++) {
                struct fletcher_4_kstat *stat = &fletcher_4_stat_data[i];
                uint64_t run_count = 0;

                /* temporary set an implementation */
                fletcher_4_impl_chosen = i;

                kpreempt_disable();
                start = gethrtime();
                do {
                        for (l = 0; l < 32; l++, run_count++)
                                fletcher_4_test(data, data_size, NULL, &zc);

                        run_time_ns = gethrtime() - start;
                } while (run_time_ns < FLETCHER_4_BENCH_NS);
                kpreempt_enable();

                run_bw = data_size * run_count * NANOSEC;
                run_bw /= run_time_ns;  /* B/s */

                if (native)
                        stat->native = run_bw;
                else
                        stat->byteswap = run_bw;

                if (run_bw > best_run) {
                        best_run = run_bw;

                        if (native) {
                                fastest_stat->native = i;
                                FLETCHER_4_FASTEST_FN_COPY(native,
                                    fletcher_4_supp_impls[i]);
                        } else {
                                fastest_stat->byteswap = i;
                                FLETCHER_4_FASTEST_FN_COPY(byteswap,
                                    fletcher_4_supp_impls[i]);
                        }
                }
        }

        /* restore original selection */
        atomic_swap_32(&fletcher_4_impl_chosen, sel_save);
}

void
fletcher_4_init(void)
{
        static const size_t data_size = 1 << SPA_OLD_MAXBLOCKSHIFT; /* 128kiB */
        fletcher_4_ops_t *curr_impl;
        char *databuf;
        int i, c;

        /* move supported impl into fletcher_4_supp_impls */
        for (i = 0, c = 0; i < ARRAY_SIZE(fletcher_4_impls); i++) {
                curr_impl = (fletcher_4_ops_t *) fletcher_4_impls[i];

                if (curr_impl->valid && curr_impl->valid())
                        fletcher_4_supp_impls[c++] = curr_impl;
        }
        membar_producer();      /* complete fletcher_4_supp_impls[] init */
        fletcher_4_supp_impls_cnt = c;  /* number of supported impl */

#if !defined(_KERNEL)
        /* Skip benchmarking and use last implementation as fastest */
        memcpy(&fletcher_4_fastest_impl,
            fletcher_4_supp_impls[fletcher_4_supp_impls_cnt-1],
            sizeof (fletcher_4_fastest_impl));
        fletcher_4_fastest_impl.name = "fastest";
        membar_producer();

        fletcher_4_initialized = B_TRUE;
        return;
#endif
        /* Benchmark all supported implementations */
        databuf = vmem_alloc(data_size, KM_SLEEP);
        for (i = 0; i < data_size / sizeof (uint64_t); i++)
                ((uint64_t *)databuf)[i] = (uintptr_t)(databuf+i); /* warm-up */

        fletcher_4_benchmark_impl(B_FALSE, databuf, data_size);
        fletcher_4_benchmark_impl(B_TRUE, databuf, data_size);

        vmem_free(databuf, data_size);

        /* install kstats for all implementations */
        fletcher_4_kstat = kstat_create("zfs", 0, "fletcher_4_bench", "misc",
                KSTAT_TYPE_RAW, 0, KSTAT_FLAG_VIRTUAL);
        if (fletcher_4_kstat != NULL) {
                fletcher_4_kstat->ks_data = NULL;
                fletcher_4_kstat->ks_ndata = UINT32_MAX;
                kstat_set_raw_ops(fletcher_4_kstat,
                    fletcher_4_kstat_headers,
                    fletcher_4_kstat_data,
                    fletcher_4_kstat_addr);
                kstat_install(fletcher_4_kstat);
        }

        /* Finish initialization */
        fletcher_4_initialized = B_TRUE;
}

void
fletcher_4_fini(void)
{
        if (fletcher_4_kstat != NULL) {
                kstat_delete(fletcher_4_kstat);
                fletcher_4_kstat = NULL;
        }
}

#if defined(_KERNEL) && defined(HAVE_SPL)
#include <linux/mod_compat.h>

static int
fletcher_4_param_get(char *buffer, zfs_kernel_param_t *unused)
{
        const uint32_t impl = IMPL_READ(fletcher_4_impl_chosen);
        char *fmt;
        int i, cnt = 0;

        /* list fastest */
        fmt = (impl == IMPL_FASTEST) ? "[%s] " : "%s ";
        cnt += sprintf(buffer + cnt, fmt, "fastest");

        /* list all supported implementations */
        for (i = 0; i < fletcher_4_supp_impls_cnt; i++) {
                fmt = (i == impl) ? "[%s] " : "%s ";
                cnt += sprintf(buffer + cnt, fmt,
                    fletcher_4_supp_impls[i]->name);
        }

        return (cnt);
}

static int
fletcher_4_param_set(const char *val, zfs_kernel_param_t *unused)
{
        return (fletcher_4_impl_set(val));
}

/*
 * Choose a fletcher 4 implementation in ZFS.
 * Users can choose "cycle" to exercise all implementations, 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 implementation.");

EXPORT_SYMBOL(fletcher_init);
EXPORT_SYMBOL(fletcher_2_incremental_native);
EXPORT_SYMBOL(fletcher_2_incremental_byteswap);
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_native_varsize);
EXPORT_SYMBOL(fletcher_4_byteswap);
EXPORT_SYMBOL(fletcher_4_incremental_native);
EXPORT_SYMBOL(fletcher_4_incremental_byteswap);
#endif