Since upgrading from Ubuntu 8.10 to 9.04, running boinc-client seems to have as increased impact on my PC.

Prior to the upgrade boinc added roughly 10 degrees C to the CPU temperatures. Since upgrading this figure is about 22 degrees C.

Any ideas as to why this might be?

The boinc version in Ubuntu 9.04 is 6.2.18 x86_64-pc-linux-gnu, the kernel is 2.6.28-11-generic on an AMD64 2GB PC.

Have you noticed any change in your application processing times?

Some versions of Ubuntu ran low-priority applications - like the science apps spawned by BOINC - in a low-power, low-speed CPU mode if nothing else on the system required waking the CPU up to full speed.

The new version may be running at full speed all the time. That would consume more input electrical power, and churn it back out again as heat energy for your air-conditioning to deal with. That would put the temperatures up.

I've not noticed any change in processing times, though I don't have records to make comparisons, and of course don't know that I'm getting the same sorts of work units.

But what you say sounds in line with what I've now found out about a change in CPU frequency scaling, since I've now found this:-
https://bugs.launchpad.net/ubuntu/+source/cpufreqd/+bug/368809
that might have something to do with it. Though if it's that, I would have expected other people to have noticed.

I'd be happier if I could revert to the previous behaviour.

My concern was that if the temperature was 54C in a fairly chilly Spring, what might it be like if we ever get any really hot weather.

Also, I had always thought (perhaps erroneously) that the lower the temperature the better, even if the chip was rated up to - say - 70C.

Actually, I think I have now found the explanation.

It seems that the default value for /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load has changed from 1 to 0, and that there also seems to be a bug such that if you change it to 1 the processor frequency is still scaled up when running a NI 19 process like Boinc.

Any ideas as to why this might be?

Maybe you were getting false readings under Ubuntu 8.10.

Maybe you're getting false readings under Ubuntu 9.04.

Maybe now you're running projects that work the CPU harder.

Maybe Ubuntu 8.10 was throttling the CPU clock and 9.04 isn't.

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I'm now pretty sure that the explanation I gave above is the right one. It looks like a kernel bug in which /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load now has no effect.