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Subject: Re: [GIT PULL] slab fixes for 3.2-rc4
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 28 Dec 2011 21:25:10 +1100
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On Wed, 2011-12-21 at 18:19 -0800, Linus Torvalds wrote:
> On Wed, Dec 21, 2011 at 9:05 AM, Tejun Heo <tj@kernel.org> wrote:
> >
> > machines.  (cc'ing arch) Does anyone have better insight here?  How
> > much more expensive are local irq save/restore compared to inc/dec'ing
> > preempt count on various archs?
> 
> I think powerpc does sw irq disable, so it's pretty much the same.

On 64-bit only, but it's probably still better than going for an atomic
op, our atomics tend to be handled at the l2 level and so are sloooow.

 .../...

> So I really suspect that we could just say: "make the irq-safe version
> be the *only* version", and no architecture will really care. Sure, it
> can be more expensive, but it usually isn't. Only when done badly and
> stupidly is it nasty.

Agreed, keep it simple, or we'll just grow more bugs like this one.

Cheers,
Ben.