Messages in this thread | | | Date | Thu, 15 Jan 2009 20:38:26 +0900 | From | Tejun Heo <> | Subject | Re: [patch] add optimized generic percpu accessors |
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Hello,
Ingo Molnar wrote: > The new ops are a pretty nice and clean solution i think. > > Firstly, accessing the current CPU is the only safe shortcut anyway (there > is where we can do %fs/%gs / rip-relative addressing modes), and the > generic per_cpu() APIs dont really provide that guarantee for us. We might > be able to hook into __get_cpu_var() but those both require to be an > lvalue and are also relatively rarely used. > > So introducing the new, rather straightforward APIs and using them > wherever they matter for performance is good. Your patchset already shaved > off an instruction from ordinary per_cpu() accesses, so it's all moving > rather close to the most-optimal situation already.
Yeah, I don't think we can do much better than those ops. I have two issues tho.
1. percpu_and() is missing. I added it for completeness's sake.
2. The generic percpu_op() should be local to the cpu, so it should expand to...
do { get_cpu_var(var) OP (val); put_cpu_var(var) } while (0)
as the original x86_OP_percpu() did. Right?
Thanks.
-- tejun
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