Kai Schaetzl wrote: > Ned Slider wrote on Sun, 03 Aug 2008 15:09:39 +0100: > >> http://www.centos.org/modules/newbb/viewtopic.php?topic_id=15484&forum=37 > > Thanks for the URL, see below! > >> Bottom line - the power saving between having frequency scaling enabled >> or not was surprisingly small (only 2-3W). It would appear that these >> processors are already fairly efficient at idle and scaling down the >> frequency adds little to the overall savings that may be obtained. > > I disagree about the reason. I think they are actually not so efficient. At > least not if I compare to a low-voltage CPU. 105 W is a lot, latest AMD > quad core low-voltage are at 50W. Did you check core temperature in the two > scaling states? It makes a huge difference for me on the AMD (which is > allowed to drop from 2500 to 1000). It drops from an already low value (30 > and 22 Celsius) by more than 10 degrees. The second core always shows the > lowest temperature (puzzle?) and it goes down to 6-8 (!) Celsius in idle > state with 1000.) I think this will also result on some more substantial > savings in Watt consumption. Even, if not, a substantially lower > temperature like this is good for a long life of all parts, anyway. > I see no difference on temps reported by coretemp for cpuspeed enabled/disabled. I *do* see a huge drop in temps between load and idle regardless of cpuspeed. > I read that thread and am puzzled by acpi-cpufreq being loaded on your > machine. If I modprobe it I get an error "device busy". Which makes sense > to me as cpufreq_ondemand (which loaded automatically) should have already > taken over. I see that behavior on all machines, no matter if Intel or AMD. >>From my research yesterday it also looks like use of acpi-cpufreq is > somewhat "older" and should not be necessary at all for newer CPUs. So, it > should be cpufreq_ondemand alone that does the scaling on your machine. Can > you confirm that? I'm not sure of the function of acpi-cpufreq. I do know that it doesn't scale back *without* cpufreq_ondemand (cpuspeed). acpi-cpufreq was autoloaded in response to enabling C1E and EIST features in the BIOS (which one is responsible I don't know as I enabled both together). > I also wonder if your machine actually scales up. You listed the output in > low/idle state. As I wrote I get the same, just at another level (they > probably think Xeon's will be active all the time, anyway, so they allow > them to drop not so much). Did you check that the frequency actually goes > up to 2400 under load? Yes, the frequency does scale up under load. I tested by launching a scientific app that loads all 4 cores at 100%. As fast as I could manually start the app and check the freq, it reported at 2.4GHz. I don't know at what point or under what load it will scale back up, and if scaling is done on a core by core basis, but it does scale back up under full load.