On Sat, 3 Nov 2007, Josh Carroll wrote:
What would be interesting to know is if the sum of the temperatures is any
different. 4BSD gets a much more random distribution of load because a
thread is run on whatever cpu context switches next. ULE will have
specific load patterns since it scans lists of cpus in a fixed order to
assign load. So that means it prefers to run on lower numbered cpus if
they are idle. This should have a side effect of allowing unused cores to
powerdown more frequently than with 4BSD although I have not verified this
in practice.
The sum of the core temperatures when the system is idle is the same
for both ULE and 4BSD. 125 C in my case (31.25 C average). Under load,
the sum (again for both) is 184 C. So you're absolutely correct, while
one core seems to get these short bursts (probably my rrd script doing
its thing), perhaps this is shared over the cores with 4BSD. The
overall temperature remains the same.
That's great to know. It would be possible to develop load balancing
algorithms that attempt to keep as many cores as possible idling without
sacraficing too much performance to improve power usage. This is
something I've been thinking about as part of load balancing and topology
improvements for 8.0.
It's important to note that temperature of individual cores may not be the
best estimate of power usage by that core since you would expect heat to
travel well across a package leading to elevated temperatures for
otherwise idle parts.
Jeff
Josh
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