Fletcher4: save/reload implementation context

Init, compute, and fini methods are changed to work on internal context object.
This is necessary because ABI does not guarantee that SIMD registers will be preserved
on function calls. This is technically the case in Linux kernel in between
`kfpu_begin()/kfpu_end()`, but it breaks user-space tests and some kernels that
don't require disabling preemption for using SIMD (osx).

Use scalar compute methods in-place for small buffers, and when the buffer size
does not meet SIMD size alignment.

Signed-off-by: Gvozden Neskovic <[email protected]>

1 files changed, 84 insertions, 62 deletions

diff --git a/module/zcommon/zfs_fletcher.c b/module/zcommon/zfs_fletcher.c
index 3ca70db13..355384f50 100644
--- a/module/zcommon/zfs_fletcher.c
+++ b/module/zcommon/zfs_fletcher.c
@@ -138,17 +138,20 @@
 #include <zfs_fletcher.h>
 
 
-static void fletcher_4_scalar_init(zio_cksum_t *zcp);
-static void fletcher_4_scalar_native(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 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"
@@ -248,22 +251,29 @@ fletcher_2_byteswap(const void *buf, uint64_t size,
 }
 
 static void
-fletcher_4_scalar_init(zio_cksum_t *zcp)
+fletcher_4_scalar_init(fletcher_4_ctx_t *ctx)
 {
-	ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0);
+	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(const void *buf, uint64_t size, zio_cksum_t *zcp)
+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 = zcp->zc_word[0];
-	b = zcp->zc_word[1];
-	c = zcp->zc_word[2];
-	d = zcp->zc_word[3];
+	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];
@@ -272,20 +282,21 @@ fletcher_4_scalar_native(const void *buf, uint64_t size, zio_cksum_t *zcp)
 		d += c;
 	}
 
-	ZIO_SET_CHECKSUM(zcp, a, b, c, d);
+	ZIO_SET_CHECKSUM(&ctx->scalar, a, b, c, d);
 }
 
 static void
-fletcher_4_scalar_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp)
+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 = zcp->zc_word[0];
-	b = zcp->zc_word[1];
-	c = zcp->zc_word[2];
-	d = zcp->zc_word[3];
+	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]);
@@ -294,7 +305,7 @@ fletcher_4_scalar_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp)
 		d += c;
 	}
 
-	ZIO_SET_CHECKSUM(zcp, a, b, c, d);
+	ZIO_SET_CHECKSUM(&ctx->scalar, a, b, c, d);
 }
 
 static boolean_t
@@ -384,13 +395,14 @@ fletcher_4_impl_get(void)
 }
 
 static inline void
-fletcher_4_native_impl(const fletcher_4_ops_t *ops, const void *buf,
-	uint64_t size, zio_cksum_t *zcp)
+fletcher_4_native_impl(const void *buf, uint64_t size, zio_cksum_t *zcp)
 {
-	ops->init_native(zcp);
-	ops->compute_native(buf, size, zcp);
-	if (ops->fini_native != NULL)
-		ops->fini_native(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*/
@@ -398,40 +410,41 @@ void
 fletcher_4_native(const void *buf, uint64_t size,
     const void *ctx_template, zio_cksum_t *zcp)
 {
-	const fletcher_4_ops_t *ops;
-	uint64_t p2size = P2ALIGN(size, 64);
+	const uint64_t p2size = P2ALIGN(size, 64);
 
 	ASSERT(IS_P2ALIGNED(size, sizeof (uint32_t)));
 
-	if (size == 0) {
+	if (size == 0 || p2size == 0) {
 		ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0);
-	} else if (p2size == 0) {
-		ops = &fletcher_4_scalar_ops;
-		fletcher_4_native_impl(ops, buf, size, zcp);
+
+		if (size > 0)
+			fletcher_4_scalar_native((fletcher_4_ctx_t *)zcp,
+			    buf, size);
 	} else {
-		ops = fletcher_4_impl_get();
-		fletcher_4_native_impl(ops, buf, p2size, zcp);
+		fletcher_4_native_impl(buf, p2size, zcp);
 
 		if (p2size < size)
-			fletcher_4_incremental_native((char *)buf + p2size,
-			    size - p2size, zcp);
+			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)
 {
-	fletcher_4_native_impl(&fletcher_4_scalar_ops, buf, size, 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 fletcher_4_ops_t *ops, const void *buf,
-	uint64_t size, zio_cksum_t *zcp)
+fletcher_4_byteswap_impl(const void *buf, uint64_t size, zio_cksum_t *zcp)
 {
-	ops->init_byteswap(zcp);
-	ops->compute_byteswap(buf, size, zcp);
-	if (ops->fini_byteswap != NULL)
-		ops->fini_byteswap(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*/
@@ -439,28 +452,29 @@ void
 fletcher_4_byteswap(const void *buf, uint64_t size,
     const void *ctx_template, zio_cksum_t *zcp)
 {
-	const fletcher_4_ops_t *ops;
-	uint64_t p2size = P2ALIGN(size, 64);
+	const uint64_t p2size = P2ALIGN(size, 64);
 
 	ASSERT(IS_P2ALIGNED(size, sizeof (uint32_t)));
 
-	if (size == 0) {
+	if (size == 0 || p2size == 0) {
 		ZIO_SET_CHECKSUM(zcp, 0, 0, 0, 0);
-	} else if (p2size == 0) {
-		ops = &fletcher_4_scalar_ops;
-		fletcher_4_byteswap_impl(ops, buf, size, zcp);
+
+		if (size > 0)
+			fletcher_4_scalar_byteswap((fletcher_4_ctx_t *)zcp,
+			    buf, size);
 	} else {
-		ops = fletcher_4_impl_get();
-		fletcher_4_byteswap_impl(ops, buf, p2size, zcp);
+		fletcher_4_byteswap_impl(buf, p2size, zcp);
 
 		if (p2size < size)
-			fletcher_4_incremental_byteswap((char *)buf + p2size,
-			    size - p2size, zcp);
+			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)
@@ -469,6 +483,13 @@ fletcher_4_incremental_combine(zio_cksum_t *zcp, const uint64_t size,
 	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] +
@@ -481,13 +502,9 @@ static inline void
 fletcher_4_incremental_impl(boolean_t native, const void *buf, uint64_t size,
     zio_cksum_t *zcp)
 {
-	static const uint64_t FLETCHER_4_INC_MAX = 8ULL << 20;
-	uint64_t len;
-
 	while (size > 0) {
 		zio_cksum_t nzc;
-
-		len = MIN(size, FLETCHER_4_INC_MAX);
+		uint64_t len = MIN(size, ZFS_FLETCHER_4_INC_MAX_SIZE);
 
 		if (native)
 			fletcher_4_native(buf, len, NULL, &nzc);
@@ -504,14 +521,22 @@ fletcher_4_incremental_impl(boolean_t native, const void *buf, uint64_t size,
 void
 fletcher_4_incremental_native(const void *buf, uint64_t size, zio_cksum_t *zcp)
 {
-	fletcher_4_incremental_impl(B_TRUE, buf, size, zcp);
+	/* 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);
 }
 
 void
 fletcher_4_incremental_byteswap(const void *buf, uint64_t size,
     zio_cksum_t *zcp)
 {
-	fletcher_4_incremental_impl(B_FALSE, buf, size, zcp);
+	/* 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);
 }
 
 
@@ -662,9 +687,6 @@ fletcher_4_init(void)
 	membar_producer();
 
 	fletcher_4_initialized = B_TRUE;
-
-	/* Use 'cycle' math selection method for userspace */
-	VERIFY0(fletcher_4_impl_set("cycle"));
 	return;
 #endif
 	/* Benchmark all supported implementations */