PowerMac G5 quad-core, CPU A1 DIODE TEMP: 90.8 C (for example): How to handle? [Mac OS X behavior]

[Mark Millard]

I've included a picture of the graph of core temperatures from Mac OS X, spanning a little over 6 minutes. The core temperature plots are colored non-black.

The "5 to 7" that I mentioned below is more like "3 to 12" over this time interval.




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Mark Millard
markmi at dsl-only.net

On 2015-Jan-17, at 02:04 PM, Mark Millard <markmi at dsl-only.net> wrote:

Mac OS X 10.5 does force idle time of some form to keep core temperatures down! My evidence is as follows.

The application Temperature monitor does show me temperature records (including graphs over time) under Mac OS X 10.5 for the G5. (No rpms.) It displays the information as for cpu A 1&2 and cpu B 1&2 (instead of 0 and 1). A2 is what it shows as a the hot one, matching FreeBSD's a1. I watched with the current short-term temperature display updating once a second (set via preferences).

Once it reached around the low 90C range on A2 the temperature on A2 started oscillating, going from the mid/low 90C's down to the 60C's/70C's and back up again, over and over, fairly rapidly. But the graph of the temperatures for all the cores shows all the CPU/core temperatures as oscillating in matching timing.

So I conclude that Mac OS X is doing something to give all the CPUs/cores time to cool down as soon as any one of them gets too hot.

So I do not expect Mac OS X to automatically power down, it has already been far longer than it takes for FreeBSD to shutdown with the patched RPM/cooling code. Menu meters shows the cores as fully used (mostly 100%, occasional 99%). They are mostly running 6 of my double/long-long HINT benchmark variants built various ways with parameter values input that are designed for long runs. (HINT is memory/CPU limited until it causes noticeable paging. But I've configured to not page with the 16GB of RAM avilable.)

So far the maximum temperature is 95.8C, and that is on A2. The next highest core is A1 at 81.2C so far. During this oscillation A2's minumum is 60.7C so far.

There is a pattern to the drops: there is a sequence of 5 to 7 in a row where the drop starts back up almost immediately but then there is a longer duration with the temperatures staying down before it starts back up again. After the longer duration drop the temperature rise is not as rapid so it is longer until the next forced-drop.

For the 5-7 in a row they tend to get somewhat closer together the further into the sequence. It may be that the time between triggers the longer cooling duration.

The G5 has been kept busy for well over an hour, far longer than FreeBSD did for "make -j 8 buildworld buildkernel"

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Mark Millard
markmi at dsl-only.net