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Subject: Re: [PATCH 01/10] random: make 'add_interrupt_randomness()' do
 something sane
From: Matt Mackall <mpm@selenic.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
        Linux Kernel Developers List <linux-kernel@vger.kernel.org>, w@1wt.eu,
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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@mit.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.