[dpdk-dev] [PATCH 2/2] eal: add u64 bit variant for reciprocal

[Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>]

Currently, rte_reciprocal only supports unsigned 32bit divisors. This
commit adds support for unsigned 64bit divisors.

Rename unsigned 32bit specific functions appropriately and update
librte_sched accordingly.

Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
---
 lib/librte_eal/bsdapp/eal/rte_eal_version.map   |   3 +-
 lib/librte_eal/common/include/rte_reciprocal.h  | 111 ++++++++++++++++++++--
 lib/librte_eal/common/rte_reciprocal.c          | 120 +++++++++++++++++++++---
 lib/librte_eal/linuxapp/eal/rte_eal_version.map |   3 +-
 lib/librte_sched/Makefile                       |   4 +-
 lib/librte_sched/rte_sched.c                    |   9 +-
 6 files changed, 222 insertions(+), 28 deletions(-)

diff --git a/lib/librte_eal/bsdapp/eal/rte_eal_version.map b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
index 00d5f60..f7f1013 100644
--- a/lib/librte_eal/bsdapp/eal/rte_eal_version.map
+++ b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
@@ -242,6 +242,7 @@ EXPERIMENTAL {
 DPDK_17.11 {
 	global:
 
-	rte_reciprocal_value;
+	rte_reciprocal_value_u32;
+	rte_reciprocal_value_u64;
 
 } DPDK_17.11;
diff --git a/lib/librte_eal/common/include/rte_reciprocal.h b/lib/librte_eal/common/include/rte_reciprocal.h
index b6d752f..fccbc09 100644
--- a/lib/librte_eal/common/include/rte_reciprocal.h
+++ b/lib/librte_eal/common/include/rte_reciprocal.h
@@ -19,25 +19,120 @@
  * to calculate the division A/B.
  */
 
+/*
+ * libdivide
+ * Copyright (C) 2010 ridiculous_fish
+ * This software is provided 'as-is', without any express or implied
+ * warranty.  In no event will the authors be held liable for any damages
+ * arising from the use of this software.
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, subject to the following restrictions:
+ *
+ * 1. The origin of this software must not be misrepresented; you must not
+ *    claim that you wrote the original software. If you use this software
+ *    in a product, an acknowledgment in the product documentation would be
+ *    appreciated but is not required.
+ *
+ * 2. Altered source versions must be plainly marked as such, and must not be
+ *    misrepresented as being the original software.
+ *
+ * 3. This notice may not be removed or altered from any source distribution.
+ *
+ * libdivide@ridiculousfish.com
+ *
+ */
+
 #ifndef _RTE_RECIPROCAL_H_
 #define _RTE_RECIPROCAL_H_
 
-#include <stdint.h>
+#include <rte_memory.h>
 
-struct rte_reciprocal {
+/**
+ * Unsigned 32-bit divisor structure.
+ */
+struct rte_reciprocal_u32 {
 	uint32_t m;
 	uint8_t sh1, sh2;
-};
+} __rte_cache_aligned;
+
+/**
+ * Unsigned 64-bit divisor structure.
+ */
+struct rte_reciprocal_u64 {
+	uint64_t m;
+	uint8_t sh1;
+} __rte_cache_aligned;
 
+/**
+ * Divide given unsigned 32-bit integer with pre calculated divisor.
+ *
+ * @param a
+ *   The 32-bit dividend.
+ * @param R
+ *   The pointer to pre calculated divisor reciprocal structure.
+ *
+ * @return
+ *   The result of the division
+ */
 static inline uint32_t
-rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R)
+rte_reciprocal_divide_u32(uint32_t a, struct rte_reciprocal_u32 *R)
+{
+	uint32_t t = (uint32_t)(((uint64_t)a * R->m) >> 32);
+
+	return (t + ((a - t) >> R->sh1)) >> R->sh2;
+}
+
+static inline uint64_t
+mullhi_u64(uint64_t x, uint64_t y)
 {
-	uint32_t t = (uint32_t)(((uint64_t)a * R.m) >> 32);
+	__uint128_t xl = x;
+	__uint128_t yl = y;
+	__uint128_t rl = xl * yl;
+	return (uint64_t)(rl >> 64);
+}
 
-	return (t + ((a - t) >> R.sh1)) >> R.sh2;
+/**
+ * Divide given unsigned 64-bit integer with pre calculated divisor.
+ *
+ * @param a
+ *   The 64-bit dividend.
+ * @param R
+ *   The pointer to pre calculated divisor reciprocal structure.
+ *
+ * @return
+ *   The result of the division
+ */
+static inline uint64_t
+rte_reciprocal_divide_u64(uint64_t a, struct rte_reciprocal_u64 *R)
+{
+	uint64_t q = mullhi_u64(R->m, a);
+	uint64_t t = ((a - q) >> 1) + q;
+	return t >> R->sh1;
 }
 
-struct rte_reciprocal
-rte_reciprocal_value(uint32_t d);
+/**
+ * Generate pre calculated divisor structure.
+ *
+ * @param d
+ *   The unsigned 32-bit divisor.
+ *
+ * @return
+ *   Divisor structure.
+ */
+struct rte_reciprocal_u32
+rte_reciprocal_value_u32(uint32_t d);
+
+/**
+ * Generate pre calculated divisor structure.
+ *
+ * @param d
+ *   The unsigned 64-bit divisor.
+ *
+ * @return
+ *   Divisor structure.
+ */
+struct rte_reciprocal_u64
+rte_reciprocal_value_u64(uint64_t d);
 
 #endif /* _RTE_RECIPROCAL_H_ */
diff --git a/lib/librte_eal/common/rte_reciprocal.c b/lib/librte_eal/common/rte_reciprocal.c
index 7ab99b4..5d7e367 100644
--- a/lib/librte_eal/common/rte_reciprocal.c
+++ b/lib/librte_eal/common/rte_reciprocal.c
@@ -31,18 +31,13 @@
  *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <stdio.h>
-#include <stdint.h>
-
-#include <rte_common.h>
-
-#include "rte_reciprocal.h"
+#include <rte_reciprocal.h>
 
 /* find largest set bit.
  * portable and slow but does not matter for this usage.
  */
 static inline int
-fls(uint32_t x)
+fls_u32(uint32_t x)
 {
 	int b;
 
@@ -54,21 +49,120 @@ fls(uint32_t x)
 	return 0;
 }
 
-struct rte_reciprocal
-rte_reciprocal_value(uint32_t d)
+struct rte_reciprocal_u32
+rte_reciprocal_value_u32(uint32_t d)
 {
-	struct rte_reciprocal R;
+	struct rte_reciprocal_u32 R;
 	uint64_t m;
 	int l;
 
-	l = fls(d - 1);
+	l = fls_u32(d - 1);
 	m = ((1ULL << 32) * ((1ULL << l) - d));
 	m /= d;
 
 	++m;
 	R.m = m;
-	R.sh1 = RTE_MIN(l, 1);
-	R.sh2 = RTE_MAX(l - 1, 0);
+	R.sh1 = l > 1 ? 1 : l;
+	R.sh2 = (l - 1 > 0) ? l - 1 : 0;
+
+	return R;
+}
+
+/* Code taken from Hacker's Delight:
+ * http://www.hackersdelight.org/HDcode/divlu.c.
+ * License permits inclusion here per:
+ * http://www.hackersdelight.org/permissions.htm
+ */
+static inline uint64_t
+divide_128_div_64_to_64(uint64_t u1, uint64_t u0, uint64_t v, uint64_t *r)
+{
+	const uint64_t b = (1ULL << 32); /* Number base (16 bits). */
+	uint64_t un1, un0,           /* Norm. dividend LSD's. */
+			 vn1, vn0,           /* Norm. divisor digits. */
+			 q1, q0,             /* Quotient digits. */
+			 un64, un21, un10,   /* Dividend digit pairs. */
+			 rhat;               /* A remainder. */
+	int s;                       /* Shift amount for norm. */
+
+    /* If overflow, set rem. to an impossible value. */
+	if (u1 >= v) {
+		if (r != NULL)
+			*r = (uint64_t) -1;
+		return (uint64_t) -1;
+	}
+
+	/* Count leading zeros. */
+	s = __builtin_clzll(v);
+	if (s > 0) {
+		v = v << s;
+		un64 = (u1 << s) | ((u0 >> (64 - s)) & (-s >> 31));
+		un10 = u0 << s;
+	} else {
+
+		un64 = u1 | u0;
+		un10 = u0;
+	}
+
+	vn1 = v >> 32;
+	vn0 = v & 0xFFFFFFFF;
+
+	un1 = un10 >> 32;
+	un0 = un10 & 0xFFFFFFFF;
+
+	q1 = un64/vn1;
+	rhat = un64 - q1*vn1;
+again1:
+	if (q1 >= b || q1*vn0 > b*rhat + un1) {
+		q1 = q1 - 1;
+		rhat = rhat + vn1;
+		if (rhat < b)
+			goto again1;
+	}
+
+	un21 = un64*b + un1 - q1*v;
+
+	q0 = un21/vn1;
+	rhat = un21 - q0*vn1;
+again2:
+	if (q0 >= b || q0*vn0 > b*rhat + un0) {
+		q0 = q0 - 1;
+		rhat = rhat + vn1;
+		if (rhat < b)
+			goto again2;
+	}
+
+	if (r != NULL)
+		*r = (un21*b + un0 - q0*v) >> s;
+	return q1*b + q0;
+}
+
+struct rte_reciprocal_u64
+rte_reciprocal_value_u64(uint64_t d)
+{
+	struct rte_reciprocal_u64 R;
+
+	const uint32_t fld = 63 - __builtin_clzll(d);
+
+	if ((d & (d - 1)) == 0) {
+		R.m = 0;
+		R.sh1 = (fld - 1) | 0x40;
+	} else {
+		uint64_t rem;
+		uint64_t multiplier;
+		uint8_t more;
+
+		multiplier = divide_128_div_64_to_64(1ULL << fld, 0, d, &rem);
+		multiplier += multiplier;
+
+		const uint64_t twice_rem = rem + rem;
+		if (twice_rem >= d || twice_rem < rem)
+			multiplier += 1;
+		more = fld;
+		R.m = 1 + multiplier;
+		R.sh1 = more | 0x40;
+	}
+
+	R.sh1 &= 0x3F;
 
 	return R;
 }
diff --git a/lib/librte_eal/linuxapp/eal/rte_eal_version.map b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
index ac68fb3..e64840c 100644
--- a/lib/librte_eal/linuxapp/eal/rte_eal_version.map
+++ b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
@@ -247,6 +247,7 @@ EXPERIMENTAL {
 DPDK_17.11 {
 	global:
 
-	rte_reciprocal_value;
+	rte_reciprocal_value_u32;
+	rte_reciprocal_value_u64;
 
 } DPDK_17.11;
diff --git a/lib/librte_sched/Makefile b/lib/librte_sched/Makefile
index 569656b..a2fd6f3 100644
--- a/lib/librte_sched/Makefile
+++ b/lib/librte_sched/Makefile
@@ -54,6 +54,8 @@ LIBABIVER := 1
 SRCS-$(CONFIG_RTE_LIBRTE_SCHED) += rte_sched.c rte_red.c rte_approx.c
 
 # install includes
-SYMLINK-$(CONFIG_RTE_LIBRTE_SCHED)-include := rte_sched.h rte_bitmap.h rte_sched_common.h rte_red.h rte_approx.h
+SYMLINK-$(CONFIG_RTE_LIBRTE_SCHED)-include := rte_sched.h rte_bitmap.h
+SYMLINK-$(CONFIG_RTE_LIBRTE_SCHED)-include += rte_sched_common.h rte_red.h
+SYMLINK-$(CONFIG_RTE_LIBRTE_SCHED)-include += rte_approx.h
 
 include $(RTE_SDK)/mk/rte.lib.mk
diff --git a/lib/librte_sched/rte_sched.c b/lib/librte_sched/rte_sched.c
index 3b8ccaa..7bb6d51 100644
--- a/lib/librte_sched/rte_sched.c
+++ b/lib/librte_sched/rte_sched.c
@@ -228,7 +228,7 @@ struct rte_sched_port {
 	uint64_t time_cpu_cycles;     /* Current CPU time measured in CPU cyles */
 	uint64_t time_cpu_bytes;      /* Current CPU time measured in bytes */
 	uint64_t time;                /* Current NIC TX time measured in bytes */
-	struct rte_reciprocal inv_cycles_per_byte; /* CPU cycles per byte */
+	struct rte_reciprocal_u32 inv_cycles_per_byte; /* CPU cycles per byte */
 
 	/* Scheduling loop detection */
 	uint32_t pipe_loop;
@@ -677,7 +677,7 @@ rte_sched_port_config(struct rte_sched_port_params *params)
 
 	cycles_per_byte = (rte_get_tsc_hz() << RTE_SCHED_TIME_SHIFT)
 		/ params->rate;
-	port->inv_cycles_per_byte = rte_reciprocal_value(cycles_per_byte);
+	port->inv_cycles_per_byte = rte_reciprocal_value_u32(cycles_per_byte);
 
 	/* Scheduling loop detection */
 	port->pipe_loop = RTE_SCHED_PIPE_INVALID;
@@ -2147,8 +2147,9 @@ rte_sched_port_time_resync(struct rte_sched_port *port)
 	uint64_t bytes_diff;
 
 	/* Compute elapsed time in bytes */
-	bytes_diff = rte_reciprocal_divide(cycles_diff << RTE_SCHED_TIME_SHIFT,
-					   port->inv_cycles_per_byte);
+	bytes_diff = rte_reciprocal_divide_u32(
+			cycles_diff << RTE_SCHED_TIME_SHIFT,
+			&port->inv_cycles_per_byte);
 
 	/* Advance port time */
 	port->time_cpu_cycles = cycles;
-- 
2.7.4