To: Arjan van de Ven <arjan@infradead.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Patch 2/6 introduce helper infrastructure
References: <20050127101117.GA9760@infradead.org>
	<20050127101228.GC9760@infradead.org>
From: Andi Kleen <ak@muc.de>
Date: Thu, 27 Jan 2005 11:41:33 +0100
In-Reply-To: <20050127101228.GC9760@infradead.org> (Arjan van de Ven's
 message of "Thu, 27 Jan 2005 10:12:28 +0000")
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Arjan van de Ven <arjan@infradead.org> writes:
> +unsigned int get_random_int(void)
> +{
> +	static unsigned int val = 0;
> +
> +	val += current->pid + jiffies;

Shouldn't there be some kind of locking for this? It's random,
but still random corruption sounds a bit too random.

Also you probably have a very hot cache line here, which
may hurt on the bigger machines.

I think it would be better to just get a global random number
for each mm as it is created and then run a fast PRNG with that
state. Maybe even make it per task to improve performance on
multithreaded programs. Or alternatively per cpu state with
different starting points.

-Andi
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