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

From: Linus Torvalds
Date: Thu Jul 05 2012 - 17:48:08 EST

On Thu, Jul 5, 2012 at 2:39 PM, Matt Mackall <mpm@xxxxxxxxxxx> wrote:
> From my read, this code path gets called on timer interrupts too.

That's hopefully never true for any normal cases (timers are *very*
special - they tend to go through their own architecture-specific
stuff). On modern PC's, for example, the timers happen through the
local apic timers directly.

In fact, with SMP, it's a really bad idea to use a normal irq for
timer interrupts, since you really really want per-CPU-core timers.

But yes, we should probably make sure that *if* the architecture uses
regular interrupts for timers we don't count them. The problematic
embedded platforms are often pretty crap hardware: even when they are
SMP, they might use an external timer irq (and then we broadcast the
thing). I think we have the IRQF_TIMER flag for that, so we could add
a check for that.

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