Re: Hotplug CPU and setaffinity?

From: Joel Schopp
Date: Mon Apr 25 2005 - 11:12:41 EST

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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