Re: Hotplug CPU and setaffinity?

[Joel Schopp <jschopp@austin.ibm.com>]

>>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.