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

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Message-ID: <20140608113000.5423.qmail@ns.horizon.com>
Date:	8 Jun 2014 07:30:00 -0400
From:	"George Spelvin" <linux@...izon.com>
To:	dborkman@...hat.com, 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

> 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:

   	/* 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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