Re: Hotplug CPU and setaffinity?

[Joel Schopp]

> > The affinity of the process is reset to the default and it is migrated
> > to another cpu, for better or worse.  The kernel assumes the admin
> > know what he/she is doing.
>
>
> Yeh that's ok - is there anything that would hotplug a cpu
> automatically; say on receiving some MCEs ; and thus not
> give the admin a look in.

On ppc64 we have CPU guard, which would remove a processor if it is 
failing.  Of course, the implications of not removing such a CPU are 
pretty terrible.

> > > In particular I was thinking of the cases where a thread has a
> > > functional reason for remaining on one particular CPU (e.g. if you
> > > had calibrated for some feature of that CPU say its time stamp
> > > counter skew/speed). Another case would be a set of threads which
> > > had set their affinity to the same CPU and then made memory
> > > consistency or locking assumptions that wouldn't be valid
> > > if they got rescheduled onto different CPUs.

This sounds like a theoretical problem.  Can you think of any real 
examples?  The only cases I can think of cause performance hits, but not 
functional problems.


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