netdev - Re: [PATCH v4 5/7] ipv6 addrconf: implement RFC7559 router solicitation backoff

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Date:   Mon, 26 Sep 2016 15:53:57 +0200
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Maciej Żenczykowski <zenczykowski@...il.com>,
        Maciej Żenczykowski <maze@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Erik Kline <ek@...gle.com>,
        Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: [PATCH v4 5/7] ipv6 addrconf: implement RFC7559 router
 solicitation backoff

On 25.09.2016 13:03, Maciej Żenczykowski wrote:
> +static inline s32 rfc3315_s14_backoff_init(s32 initial)
> +{
> +	u32 r = (9 << 20) / 10 + (prandom_u32() % ((2 << 20) / 10 + 1));

^

> +	s32 v = initial * (u64)r >> 20;       /* ~ multiply by 0.9 .. 1.1 */
> +	return v;
> +}
> +
> +static inline s32 rfc3315_s14_backoff_update(s32 cur, s32 ceiling)
> +{
> +	u32 r = (19 << 20) / 10 + (prandom_u32() % ((2 << 20) / 10 + 1));

Please just use do_div here and go back to the first version of the
patch. Variable names could be more aligned with the RFC maybe?

> +	s32 v = cur * (u64)r >> 20;           /* ~ multiply by 1.9 .. 2.1 */
> +	if (v > ceiling) {
> +		r -= 1 << 20;
> +		v = ceiling * (u64)r >> 20;   /* ~ multiply by 0.9 .. 1.1 */
> +	}
> +	return v;
> +}

Thanks,
Hannes