Messages in this thread | | | Date | Fri, 16 Jan 2009 23:09:25 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] percpu: add optimized generic percpu accessors |
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* Rusty Russell <rusty@rustcorp.com.au> wrote:
> On Friday 16 January 2009 10:42:00 Herbert Xu wrote: > > Ingo Molnar <mingo@elte.hu> wrote: > > > > > >> Of course. But do any architectures actually _need_ that for a single > > >> read? > > > > > > not for a read i guess - but for the other ops like add/and/or/xor. > > > > One of the things I'd like to see happen with this work is for > > us to have a cheap per-cpu atomic counter that we can use for > > SNMP stats. > > > > If we can make the inc/add variants into a single instruction, then it > > won't need to disable preemption or interrupts. > > > > So if you could design the API such that we have a variant of add/inc > > that automatically disables/enables preemption then we can optimise > > that away on x86. > > Yep, already on it. It's called local_t; that's what it was originally > designed for. > > Unfortunately, to use it efficiently, we need large per-cpu areas.
This makes no sense to me at all. Care to explain?
Ingo
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