Skip to content
Permalink
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: David 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: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
  • Loading branch information
borkmann authored and davem330 committed Jan 22, 2014
1 parent f337db6 commit 89770b0a69ee0e0e5e99c722192d535115f73778
Showing with 21 additions and 5 deletions.
  1. +19 −0 include/linux/kernel.h
  2. +1 −3 include/net/codel.h
  3. +1 −2 net/packet/af_packet.c
@@ -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);
@@ -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,
@@ -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,

0 comments on commit 89770b0

Please sign in to comment.
You can’t perform that action at this time.