Commit 89770b0a authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

net: introduce reciprocal_scale helper and convert users 

As David Laight suggests, we shouldn't necessarily call this
reciprocal_divide() when users didn't requested a reciprocal_value();
lets keep the basic idea and call it reciprocal_scale(). More
background information on this topic can be found in [1].

Joint work with Hannes Frederic Sowa.

  [1] http://homepage.cs.uiowa.edu/~jones/bcd/divide.html



Suggested-by: default avatarDavid Laight <david.laight@aculab.com>
Cc: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f337db64

include/linux/kernel.h

+19 −0
Original line number Diff line number Diff line
@@ -193,6 +193,25 @@ extern int _cond_resched(void); 
		(__x < 0) ? -__x : __x;		\

	})



/**

 * reciprocal_scale - "scale" a value into range [0, ep_ro)

 * @val: value

 * @ep_ro: right open interval endpoint

 *

 * Perform a "reciprocal multiplication" in order to "scale" a value into

 * range [0, ep_ro), where the upper interval endpoint is right-open.

 * This is useful, e.g. for accessing a index of an array containing

 * ep_ro elements, for example. Think of it as sort of modulus, only that

 * the result isn't that of modulo. ;) Note that if initial input is a

 * small value, then result will return 0.

 *

 * Return: a result based on val in interval [0, ep_ro).

 */

static inline u32 reciprocal_scale(u32 val, u32 ep_ro)

{

	return (u32)(((u64) val * ep_ro) >> 32);

}



#if defined(CONFIG_MMU) && \

	(defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP))

void might_fault(void);

include/net/codel.h

+1 −3
Original line number Diff line number Diff line
@@ -46,7 +46,6 @@ 
#include <linux/skbuff.h>

#include <net/pkt_sched.h>

#include <net/inet_ecn.h>

#include <linux/reciprocal_div.h>



/* Controlling Queue Delay (CoDel) algorithm

 * =========================================
@@ -211,10 +210,9 @@ static codel_time_t codel_control_law(codel_time_t t, 
				      codel_time_t interval,

				      u32 rec_inv_sqrt)

{

	return t + reciprocal_divide(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);

	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);

}





static bool codel_should_drop(const struct sk_buff *skb,

			      struct Qdisc *sch,

			      struct codel_vars *vars,

net/packet/af_packet.c

+1 −2
Original line number Diff line number Diff line
@@ -88,7 +88,6 @@ 
#include <linux/virtio_net.h>

#include <linux/errqueue.h>

#include <linux/net_tstamp.h>

#include <linux/reciprocal_div.h>

#include <linux/percpu.h>

#ifdef CONFIG_INET

#include <net/inet_common.h>
@@ -1262,7 +1261,7 @@ static unsigned int fanout_demux_hash(struct packet_fanout *f, 
				      struct sk_buff *skb,

				      unsigned int num)

{

	return reciprocal_divide(skb->rxhash, num);

	return reciprocal_scale(skb->rxhash, num);

}



static unsigned int fanout_demux_lb(struct packet_fanout *f,

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