netdev - Re: [PATCH net-next] filter: add bpf_optimize

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Message-ID: <546E5DE9.3050602@redhat.com>
Date:	Thu, 20 Nov 2014 22:32:25 +0100
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Denis Kirjanov <kda@...ux-powerpc.org>
CC:	netdev@...r.kernel.org, Alexei Starovoitov <ast@...mgrid.com>
Subject: Re: [PATCH net-next] filter: add bpf_optimize_div()

On 11/20/2014 08:42 PM, Denis Kirjanov wrote:
> optimize_div() found in  mips bpf jit is really usefull
> for other arches. So let's put it in filter.h
>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> Signed-off-by: Denis Kirjanov <kda@...ux-powerpc.org>

NAK

1) There's no user of this function (you name MIPS JIT, but
    don't remove it from there) ...

2) It's not really specific or tied to the BPF API in particular,
    so doesn't really belong here, rather some more generic kernel
    header, iff anything.

> ---
>   include/linux/filter.h | 11 +++++++++++
>   1 file changed, 11 insertions(+)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index ca95abd..b385637 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -414,6 +414,17 @@ static inline void bpf_jit_dump(unsigned int flen, unsigned int proglen,
>   		print_hex_dump(KERN_ERR, "JIT code: ", DUMP_PREFIX_OFFSET,
>   			       16, 1, image, proglen, false);
>   }
> +
> +static inline int bpf_optimize_div(u32 *k)
> +{
> +	/* power of 2 divides can be implemented with right shift */
> +	if (!(*k & (*k-1))) {
> +		*k = ilog2(*k);
> +		return 1;
> +	}
> +
> +	return 0;
> +}
>   #else
>   static inline void bpf_jit_compile(struct bpf_prog *fp)
>   {
>
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