From c26aed40f4fd18f86bcc6aba557cab700b129b73 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 18 Nov 2010 22:04:46 +0000
Subject: [PATCH] filter: use reciprocal divide
At compile time, we can replace the DIV_K instruction (divide by a
constant value) by a reciprocal divide.
At exec time, the expensive divide is replaced by a multiply, a less
expensive operation on most processors.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/core/filter.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index c0b68f7c8036..23e0a2a9a4de 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -37,6 +37,7 @@
#include <asm/uaccess.h>
#include <asm/unaligned.h>
#include <linux/filter.h>
+#include <linux/reciprocal_div.h>
enum {
BPF_S_RET_K = 1,
@@ -205,7 +206,7 @@ unsigned int sk_run_filter(struct sk_buff *skb, const struct sock_filter *fentry
A /= X;
continue;
case BPF_S_ALU_DIV_K:
- A /= K;
+ A = reciprocal_divide(A, K);
continue;
case BPF_S_ALU_AND_X:
A &= X;
@@ -506,6 +507,7 @@ int sk_chk_filter(struct sock_filter *filter, int flen)
/* check for division by zero */
if (ftest->k == 0)
return -EINVAL;
+ ftest->k = reciprocal_value(ftest->k);
break;
case BPF_S_LD_MEM:
case BPF_S_LDX_MEM:
--
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