Re: 2.6.16-rc6-mm2

[Nick Piggin <nickpiggin@yahoo.com.au>]

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.

--
SUSE Labs, Novell Inc.
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