[dpdk-dev] [PATCH v6 2/3] eal: add u64 bit variant for reciprocal

Dumitrescu, Cristian cristian.dumitrescu at intel.com
Wed Sep 20 15:15:29 CEST 2017


Hi Pavan,

Same ask as for the first patch:
-Do not change existing code in rte_reciprocal.[hc]: no _u32 suffix, please
-Do not add lots of CR+LF to existing code

> -----Original Message-----
> From: Pavan Nikhilesh [mailto:pbhagavatula at caviumnetworks.com]
> Sent: Wednesday, September 6, 2017 11:22 AM
> To: Dumitrescu, Cristian <cristian.dumitrescu at intel.com>;
> stephen at networkplumber.org
> Cc: dev at dpdk.org; Pavan Bhagavatula
> <pbhagavatula at caviumnetworks.com>
> Subject: [dpdk-dev] [PATCH v6 2/3] eal: add u64 bit variant for reciprocal
> 
> From: Pavan Bhagavatula <pbhagavatula at 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 at caviumnetworks.com>
> ---
>  lib/librte_eal/bsdapp/eal/rte_eal_version.map   |   3 +-
>  lib/librte_eal/common/include/rte_reciprocal.h  | 109
> ++++++++++++++++++++--
>  lib/librte_eal/common/rte_reciprocal.c          | 116
> +++++++++++++++++++++---
>  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, 219 insertions(+), 25 deletions(-)
> 
> diff --git a/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> index 90d7258..59a85bb 100644
> --- a/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> +++ b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> @@ -241,6 +241,7 @@ EXPERIMENTAL {
>  DPDK_17.11 {
>  	global:
> 
> -	rte_reciprocal_value;
> +	rte_reciprocal_value_u32;
> +	rte_reciprocal_value_u64;
> 
>  } DPDK_17.08;
> diff --git a/lib/librte_eal/common/include/rte_reciprocal.h
> b/lib/librte_eal/common/include/rte_reciprocal.h
> index b6d752f..85599e6 100644
> --- a/lib/librte_eal/common/include/rte_reciprocal.h
> +++ b/lib/librte_eal/common/include/rte_reciprocal.h
> @@ -22,22 +22,117 @@
>  #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;
>  };
> 

Do not add _32 suffix for exiting function, no name change, please.

> +/**
> + * Unsigned 64-bit divisor structure.
> + */
> +struct rte_reciprocal_u64 {
> +	uint64_t m;
> +	uint8_t sh1;
> +};
> +

I am OK with adding +64 suffix for new API.

> +/**
> + * 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);
> +	uint32_t t = (((uint64_t)a * R->m) >> 32);
> 
> -	return (t + ((a - t) >> R.sh1)) >> R.sh2;
> +	return (t + ((a - t) >> R->sh1)) >> R->sh2;
>  }

Do not add _u32 suffix for existing API.

> 
> -struct rte_reciprocal
> -rte_reciprocal_value(uint32_t d);
> +static inline uint64_t
> +mullhi_u64(uint64_t x, uint64_t y)
> +{
> +#ifdef __SIZEOF_INT128__
> +	__uint128_t xl = x;
> +	__uint128_t rl = xl * y;
> +
> +	return (rl >> 64);
> +#else
> +	uint64_t u0, u1, v0, v1, k, t;
> +	uint64_t w1, w2;
> +	uint64_t whi;
> +
> +	u1 = x >> 32; u0 = x & 0xFFFFFFFF;
> +	v1 = y >> 32; v0 = y & 0xFFFFFFFF;
> +
> +	t = u0*v0;
> +	k = t >> 32;
> +
> +	t = u1*v0 + k;
> +	w1 = t & 0xFFFFFFFF;
> +	w2 = t >> 32;
> +
> +	t = u0*v1 + w1;
> +	k = t >> 32;
> +
> +	whi = u1*v1 + w2 + k;
> +
> +	return whi;
> +#endif
> +}
> +
> +/**
> + * 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;
> +}
> +
> +/**
> + * 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);
> +

Do not add _u32 suffix for existing API.

> +/**
> + * 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..2024e62 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;
> 
> @@ -54,14 +49,14 @@ fls(uint32_t x)
>  	return 0;
>  }
> 

Do not add _u32 suffix for existing API.

> -struct rte_reciprocal
> -rte_reciprocal_value(uint32_t d)
> +struct rte_reciprocal_u32
> +rte_reciprocal_value_u32(uint32_t d)

Do not add _u32 suffix for existing API.

>  {
> -	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;
> 
> @@ -72,3 +67,102 @@ rte_reciprocal_value(uint32_t d)
> 
>  	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 2070cba..2671627 100644
> --- a/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> +++ b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> @@ -246,6 +246,7 @@ EXPERIMENTAL {
>  DPDK_17.11 {
>  	global:
> 
> -	rte_reciprocal_value;
> +	rte_reciprocal_value_u32;

Do not add _u32 suffix for existing API.

> +	rte_reciprocal_value_u64;
> 
>  } DPDK_17.08;
> 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);
> 

Do not add _u32 suffix for existing API.

>  	/* 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(

Do not add _u32 suffix for existing API.

> +			cycles_diff << RTE_SCHED_TIME_SHIFT,
> +			&port->inv_cycles_per_byte);
> 
>  	/* Advance port time */
>  	port->time_cpu_cycles = cycles;
> --
> 2.7.4



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