diff options
| author | Daniel Borkmann <dborkman@redhat.com> | 2014-01-22 02:29:40 +0100 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-01-21 23:17:20 -0800 |
| commit | 89770b0a69ee0e0e5e99c722192d535115f73778 (patch) | |
| tree | a8c96a91c2417dc81f5ce08aa59ebcfd456e0335 | |
| parent | f337db64af059c9a94278a8b0ab97d87259ff62f (diff) | |
| download | lwn-89770b0a69ee0e0e5e99c722192d535115f73778.tar.gz lwn-89770b0a69ee0e0e5e99c722192d535115f73778.zip | |
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>
| -rw-r--r-- | include/linux/kernel.h | 19 | ||||
| -rw-r--r-- | include/net/codel.h | 4 | ||||
| -rw-r--r-- | net/packet/af_packet.c | 3 |
3 files changed, 21 insertions, 5 deletions
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index ecb87544cc5d..03d8a6b0e2e8 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -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); diff --git a/include/net/codel.h b/include/net/codel.h index 3b04ff5f6f8d..fe0eab32ce76 100644 --- a/include/net/codel.h +++ b/include/net/codel.h @@ -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, diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index df3cbdd585c7..97346162803d 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -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, |