Re: [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one, take#2
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- To: Peter Chubb <peterc@xxxxxxxxxxxxxxxxxx>
- Subject: Re: [PATCHSET percpu#for-next] percpu: convert ia64 to dynamic percpu and drop the old one, take#2
- From: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 30 Sep 2009 19:49:50 -0400 (EDT)
- Cc: "Luck, Tony" <tony.luck@xxxxxxxxx>, 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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On Thu, 1 Oct 2009, Peter Chubb wrote:
> 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.
Dynamic and static per cpu variables could use relative access to that
register. This would reduce code size, avoid the use of a TLB entry.
> You';d have to do somne careful benchmarking on a wide variety of
> workloads and machines to get a definitive answer.
I have some patches here that make heavy use of dynamic percpu allocations
in the allocators to optimize the alloc / free paths.
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