Re: 2.6.16-rc6-mm2

Nick Piggin
2006-06-13T05:43:18Z

Andi Kleen wrote:
> On Tuesday 13 June 2006 07:08, Keith Owens wrote:
>
>>Andi Kleen (on Tue, 13 Jun 2006 06:56:45 +0200) wrote:
>>
>>>>I have previously suggested a lightweight solution that pins a process
>>>>to a cpu
>>>
>>>That is preempt_disable()/preempt_enable() effectively
>>>It's also light weight as much as these things can be.
>>
>>The difference being that preempt_disable() does not allow the code to
>>sleep. There are some places where we want to use cpu local data
>>and
>>the code can tolerate preemption and even sleeping, as long as the
>>process schedules back on the same cpu.
>
>
> Seems like a pretty obscure case to optimize for.
>
> Anyways if you want to do that you can always do
>
> disable_preempt();
> set thread affinity mask to current cpu
> enable_preempt();
> do weird stuff and sleep ... ;
> restore affinity mask
>
> Can any of these people proposing "solutions" in this thread
> demonstrate this stuff is actually performance critical?

You can't do this in general, because CPU hotplug will reset the
affinity mask if the CPU is unplugged. I'd just say: don't do that.

However you can get some similar functionality by putting stuff in
task_struct.

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SUSE Labs, Novell Inc.
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