Re: Hotplug CPU and setaffinity?

From: Dave Gilbert (Home)
Date: Mon Apr 25 2005 - 12:36:17 EST

Joel Schopp wrote:

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.

Well I'm not aware of anything that currently would break with it; but I was gently thinking of whether it would be possible to read cycle counters (as a faster gettimeofday) even on systems which had unsynchronised counters if you could lock the thread that did it to a particular physical cpu.
But this behaviour currently makes that a bad idea; in this case it would be nicer if the kernel either just killed my process or just unscheduled it or sent it a signal.

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