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

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Message-ID: <20120706165257.GD10798@thunk.org>
Date:	Fri, 6 Jul 2012 12:52:57 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Matt Mackall <mpm@...enic.com>,
	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 Fri, Jul 06, 2012 at 09:24:00AM -0700, Linus Torvalds wrote:
> On Fri, Jul 6, 2012 at 6:01 AM, Theodore Ts'o <tytso@....edu> wrote:
> > What in the world is "fast count"?  I've grepped for it,
> > and I can't find it.
> 
> It's your own fast-pool counter that Matt was talking about.

When he said "check it against HZ", it confused me, since there's no
way to compare it against HZ.  But yes, I can certainly not give any
credit for entropy if __IRQF_TIMER is set, or keep track of whether
the previous interrupt had __IRQF_TIMER set in its descriptor.  That's
simple enough.

I thought he was saying there was some way to distinguish between
interrupts triggered by the clock interrupt versus other devices on
the same irq channel --- and I couldn't figure out any to do that in
an architecture independent way.

					- Ted

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