netdev - Re: [PATCH net] sch_tbf: use do

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Date:	Thu, 12 Dec 2013 17:21:18 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Yang Yingliang <yangyingliang@...wei.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH net] sch_tbf: use do_div() for 64-bit divide

Hello.

On 12-12-2013 6:22, Yang Yingliang wrote:

> It's doing a 64-bit divide which is not supported
> on 32-bit architectures in psched_ns_t2l(). The
> correct way to do this is to use do_div().

> Reported-by: kbuild test robot <fengguang.wu@...el.com>
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
>   net/sched/sch_tbf.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)

> diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
> index a44928c..887e672 100644
> --- a/net/sched/sch_tbf.c
> +++ b/net/sched/sch_tbf.c
> @@ -131,8 +131,10 @@ static u64 psched_ns_t2l(const struct psched_ratecfg *r,
>
>   	do_div(len, NSEC_PER_SEC);
>
> -	if (unlikely(r->linklayer == TC_LINKLAYER_ATM))
> -		len = (len / 53) * 48;
> +	if (unlikely(r->linklayer == TC_LINKLAYER_ATM)) {
> +		do_div(len, 53);
> +		len = len * 48;

    Why not simply len *= 48? You're coding in C, after all. :-)

WBR, Sergei

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