Messages in this thread | | | Date | Thu, 01 Oct 2009 09:06:33 +1000 | From | Peter Chubb <> | Subject | Re: [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one, take#2 |
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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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