Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 5 Jul 2012 19:59:00 -0700 | Subject | Re: [PATCH 01/10] random: make 'add_interrupt_randomness()' do something sane |
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On Thu, Jul 5, 2012 at 4:21 PM, Theodore Ts'o <tytso@mit.edu> wrote: > On Thu, Jul 05, 2012 at 05:31:22PM -0500, Matt Mackall wrote: >> >> 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. > > I'm not sure what you mean by this?
So what I think Matt meant was to check number of timer interrupts against the fast count.
IOW, always call "add_interrupt_randomness()", but then in that function, when you determine the amount of entropy, check if there were non-timer interrupts in the last HZ cycle. If there were purely timer interrupts, you can still mix in the cycle information, but it's likely to be fairly weak.
That said, if we do have a real TSC, I suspect there's tons of entropy in it even for a pure timer interrupt, so it's more like "if the *only* source of randomness we have is the timer interrupt and the jiffies value, that doesn't really add any entropy at all".
Linus
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