Re: [PATCH 01/10] random: make 'add_interrupt_randomness()' dosomething sane

From: Matt Mackall
Date: Thu Jul 05 2012 - 17:39:45 EST

On Thu, 2012-07-05 at 11:52 -0700, Linus Torvalds wrote:
> On Thu, Jul 5, 2012 at 11:47 AM, Matt Mackall <mpm@xxxxxxxxxxx> wrote:
> >
> > I think you should demand a minimum number of events > HZ to actually
> > credit any valid entropy.
> There already is. It's 1.

> If we don't get a single non-timer interrupt, this code will never be called.

>From my read, this code path gets called on timer interrupts too. Thus
the number of events per HZ will be HZ at a minimum on systems that
haven't gone tickless. If such systems a) don't have a higher-res time
source and b) are halted or equivalent, such samples will be completely
deterministic. So the threshold for crediting entropy should be HZ + 1.

But perhaps I've missed something.

(As I expressed in my last message, this is strictly a correctness issue
and not a practical one. I've long held that the entropy counting model
is bogus and should be abandoned.)

Mathematics is the supreme nostalgia of our time.

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