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Re: Proposal: HAVE_SEPARATE_IRQ_STACK?

From "Jason A. Donenfeld" <Jason@zx2c4.com>
Newsgroups linux.kernel
Subject Re: Proposal: HAVE_SEPARATE_IRQ_STACK?
Date 2016-11-10 00:40 +0100
Message-ID <sBKDf-5OO-1@gated-at.bofh.it> (permalink)
References <sBIBr-4hw-9@gated-at.bofh.it> <sBIUO-4sZ-5@gated-at.bofh.it>
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Hey Thomas,

On Wed, Nov 9, 2016 at 10:40 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> That preempt_disable() prevents merily preemption as the name says, but it
> wont prevent softirq handlers from running on return from interrupt. So
> what's the point?

Oh, interesting. Okay, then in that case the proposed define wouldn't
be useful for my purposes. What clever tricks do I have at my
disposal, then?

>> If not, do you have a better solution for me (which doesn't
>> involve using kmalloc or choosing a different crypto primitive)?
>
> What's wrong with using kmalloc?

It's cumbersome and potentially slow. This is crypto code, where speed
matters a lot. Avoiding allocations is usually the lowest hanging
fruit among optimizations. To give you some idea, here's a somewhat
horrible solution using kmalloc I hacked together: [1]. I'm not to
happy with what it looks like, code-wise, and there's around a 16%
slowdown, which isn't nice either.

[1] https://git.zx2c4.com/WireGuard/commit/?h=jd/curve25519-kmalloc

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Thread

Proposal: HAVE_SEPARATE_IRQ_STACK? "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-09 22:30 +0100
  Re: Proposal: HAVE_SEPARATE_IRQ_STACK? Thomas Gleixner <tglx@linutronix.de> - 2016-11-09 22:50 +0100
    Re: Proposal: HAVE_SEPARATE_IRQ_STACK? "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-10 00:40 +0100
      Re: Proposal: HAVE_SEPARATE_IRQ_STACK? Thomas Gleixner <tglx@linutronix.de> - 2016-11-10 10:10 +0100
        Re: Proposal: HAVE_SEPARATE_IRQ_STACK? "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-10 12:50 +0100
          Re: Proposal: HAVE_SEPARATE_IRQ_STACK? Thomas Gleixner <tglx@linutronix.de> - 2016-11-10 14:10 +0100
            Re: Proposal: HAVE_SEPARATE_IRQ_STACK? "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-10 18:50 +0100
          Re: Proposal: HAVE_SEPARATE_IRQ_STACK? Matt Redfearn <matt.redfearn@imgtec.com> - 2016-11-10 17:40 +0100
            Re: Proposal: HAVE_SEPARATE_IRQ_STACK? "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-10 18:40 +0100
  Re: Proposal: HAVE_SEPARATE_IRQ_STACK? "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-11-10 02:50 +0100

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