linux-kernel - Re: [PATCH 6/7] lib/random32.c: Randomize timeout to the millisecond, not the second

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Date:	Sun, 08 Jun 2014 14:28:13 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	George Spelvin <linux@...izon.com>
CC:	davem@...emloft.net, hannes@...essinduktion.org,
	linux-kernel@...r.kernel.org, shemminger@...l.org, tytso@....edu
Subject: Re: [PATCH 6/7] lib/random32.c: Randomize timeout to the millisecond,
 not the second

On 06/08/2014 01:30 PM, George Spelvin wrote:
>> Fine by me this cleanup, although not strictly needed.
>
> Agreed.  The timer slack is set to HZ (1 second) anyway.
>
> It just dawned on me that a simpler and more efficient way to do this
> (which I'll do in v2 of this) would be:

Note, when you talk about efficiency here, this is called once every
40+ secs ... ;)

>     	/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
> -	expires = 40 + (prandom_u32() % 40);
> -	seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);
> +	expires = 40*HZ + prandom_u32_max(40*HZ);
> +	seed_timer.expires = jiffies + expires;
>
> That avoids calling msecs_to_jiffies entirely.
>
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