From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Frederic Sowa Subject: [PATCH net-next v4 2/3] net: introduce reciprocal_scale helper and convert users Date: Wed, 22 Jan 2014 02:02:29 +0100 Message-ID: <1390352550-4511-3-git-send-email-hannes@stressinduktion.org> References: <1390352550-4511-1-git-send-email-hannes@stressinduktion.org> Cc: Daniel Borkmann , Jakub Zawadzki , Eric Dumazet , linux-kernel@vger.kernel.org To: netdev@vger.kernel.org Return-path: In-Reply-To: <1390352550-4511-1-git-send-email-hannes@stressinduktion.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Daniel Borkmann 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 Cc: Jakub Zawadzki Cc: Eric Dumazet Cc: linux-kernel@vger.kernel.org Signed-off-by: Hannes Frederic Sowa Signed-off-by: Daniel Borkmann --- include/linux/kernel.h | 19 +++++++++++++++++++ include/net/codel.h | 4 +--- 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 ecb8754..03d8a6b 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 3b04ff5..fe0eab3 100644 --- a/include/net/codel.h +++ b/include/net/codel.h @@ -46,7 +46,6 @@ #include #include #include -#include /* 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 df3cbdd..9734616 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -88,7 +88,6 @@ #include #include #include -#include #include #ifdef CONFIG_INET #include @@ -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, -- 1.8.4.2