| Submitter | Eric Dumazet |
|---|---|
| Date | Nov. 19, 2010, 8:04 a.m. |
| Message ID | <1290153886.29509.10.camel@edumazet-laptop> |
| Download | mbox | patch |
| Permalink | /patch/72224/ |
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
Comments
On Fri, Nov 19, 2010 at 4:04 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > 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>
From: Changli Gao <xiaosuo@gmail.com> Date: Fri, 19 Nov 2010 16:18:05 +0800 > On Fri, Nov 19, 2010 at 4:04 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote: >> 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> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Patch
diff --git a/net/core/filter.c b/net/core/filter.c index a1edb5d..13853c7 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, @@ -202,7 +203,7 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int A /= X; continue; case BPF_S_ALU_DIV_K: - A /= f_k; + A = reciprocal_divide(A, f_k); continue; case BPF_S_ALU_AND_X: A &= X; @@ -503,6 +504,7 @@ 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:
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> --- net/core/filter.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html