Re: [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one, take#2
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- To: "Luck, Tony" <tony.luck@xxxxxxxxx>
- Subject: Re: [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one, take#2
- From: Peter Chubb <peterc@xxxxxxxxxxxxxxxxxx>
- Date: Thu, 01 Oct 2009 09:06:33 +1000
- Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>, Tejun Heo <teheo@xxxxxxx>, Nick Piggin <npiggin@xxxxxxx>, "Yu, Fenghua" <fenghua.yu@xxxxxxxxx>, linux-ia64 <linux-ia64@xxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>
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>>>>> "Tony" == Tony Luck <Luck> writes:
>> Tony: Could we use a global register for the per cpu address? That
>> would make IA64 work similar to sparc.
Tony> Would that be a useful trade of resources for convenience?
Tony> We've already hard-wired r13 for "current". Grabbing another one
Tony> would require fixing (since user code will have clobbered it).
Tony> Possibly re-working any existing code that already uses whatever
Tony> register you choose.
r3, r4 and r5 are currently unused by the kernel, and unused
by GCC and ICC. Only hand-written assembler and weird compilers use
those registers(and my virtual-machine monitor :-(). If you wanted to
experiment, that'd be a starting place.
I'm not sure of the advantage though -- TLB mapping is relatively
cheap, and we're no longer hard-wiring the translation register.
You';d have to do somne careful benchmarking on a wide variety of
workloads and machines to get a definitive answer.
---
Dr Peter Chubb www.nicta.com.au peter DOT chubb AT nicta.com.au
http://www.ertos.nicta.com.au ERTOS within National ICT Australia
>From Imagination to Impact Imagining the (ICT) Future
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