linux-kernel - Re: [PATCH 01/10] random: make 'add_interrupt

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Date:	Thu, 05 Jul 2012 17:31:22 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Theodore Ts'o <tytso@....edu>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	w@....eu, ewust@...ch.edu, zakir@...ch.edu, greg@...ah.com,
	nadiah@...ucsd.edu, jhalderm@...ch.edu, tglx@...utronix.de,
	davem@...emloft.net, stable@...nel.org
Subject: Re: [PATCH 01/10] random: make 'add_interrupt_randomness()' do
 something sane

On Thu, 2012-07-05 at 15:21 -0700, Linus Torvalds wrote:
> On Thu, Jul 5, 2012 at 3:00 PM, Theodore Ts'o <tytso@....edu> wrote:
> >
> > Like this?
> 
> Looks fine to me.
> 
> Although I think it might be better to stay closer to what we used to
> do, and just 'or' in the action flags rather than make it some
> conditional. And then at the end, do
> 
>    if (!(flags & __IRQF_TIMER))
>       add_interrupt_randomness(irq)

On systems with a timer interrupt and a sched_clock() that's
asynchronous to it, this actually loses a great source of entropy for
headless systems. Also: extra branch in fast path.

It's better to mix and not credit than to not mix at all. Instead just
check the fast count against HZ before the credit.

-- 
Mathematics is the supreme nostalgia of our time.


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