linux-kernel - RE: [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one, take#2

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Date:	Wed, 30 Sep 2009 15:05:43 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Tejun Heo <teheo@...e.de>, Nick Piggin <npiggin@...e.de>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	linux-ia64 <linux-ia64@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic
 percpu and drop the old one, take#2

> Tony: Could we use a global register for the per cpu address? That would
> make IA64 work similar to sparc.

Would that be a useful trade of resources for convenience?  We've already
hard-wired r13 for "current". Grabbing another one would require fixing
(since user code will have clobbered it).  Possibly re-working any existing
code that already uses whatever register you choose.

How would that compare with using [r13]?

We might have a krN free ... but kregs are a lot slower than real registers.

-Tony
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