Re: is minimum udelay() not respected in preemptible SMP kernel-2.6.23?

[Avi Kivity]

Andi Kleen wrote:
> On Thursday 08 November 2007 01:20, Matt Mackall wrote:
>   
> > On Wed, Nov 07, 2007 at 12:30:45PM -0800, Andrew Morton wrote:
> >     
> > > Ow.  Yes, from my reading delay_tsc() can return early (or after
> > > heat-death-of-the-universe) if the TSCs are offset and if preemption
> > > migrates the calling task between CPUs.
> > >
> > > I suppose a lameo fix would be to disable preemption in delay_tsc().
> > >       
> > preempt_disable is lousy documentation here. This and other cases
> > (lots of per_cpu users, IIRC) actually want a migrate_disable() which
> > is a proper subset. We can simply implement migrate_disable() as
> > preempt_disable() for now and come back later and implement a proper
> > migrate_disable() that still allows preemption (and thus avoids the
> > latency).
> >     
>
> We could actually do this right now. migrate_disable() can be just changing
> the cpu affinity of the current thread to current cpu and then restoring it 
> afterwards. That should even work from interrupt context.
>
> get_cpu() etc. could be changed to use this then too.
>
>   

What if some other thread calls sched_setaffinity() on the 
migrate_disable()d cpu?  we'd need to detect this to avoid 
migrate_enable() stomping on sched_setaffinity()'s work.


--
error compiling committee.c: too many arguments to function

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