On 07/19/2011 11:07 AM, Eric Sandeen wrote: > On 07/19/2011 09:59 AM, Jaroslav Skarvada wrote:
>> Sad that the daemon gone. It was able to dynamically switch speed >> (and save power) on systems that have CPUs with high transition >> latency (e.g. old P4, some Atoms, etc.). On such systems the > > Actually, no... > > http://codemonkey.org.uk/2009/01/18/forthcoming-p4clockmod/ > >> So the 1.00GHz ‘frequency’ is actually “run at 2GHz, but only do work 50% of >> the time”. >> >> On the surface, this sounds like a good idea. The other 50%, the CPU is >> idle, so you’re saving power, right? >> Not so much. In fact, you could be burning more power. The reason for this >> is that when the processor is sitting there doing nothing, it isn’t lower >> frequency, and more importantly, it very likely isn’t entering C states. So >> you’re burning the same amount of power, but now you’re only doing work for >> 50% of the time. As a result of this, your workload takes twice as long to >> complete. > > I've measured it, and Dave is right. You might get something saying > "1.0Ghz" but you're not saving anything at all. There are second-order effects---the processor probably doesn't use significantly less power but the graphic card and chipset do, for some overall system effects---people quoted numbers like 20% battery savings for 50% slowdown (if p4_clockmod really stopped the CPU 50% of the time, it'd double the battery life, so this really is a very inefficient and crude method). -- devel mailing list devel@lists.fedoraproject.org https://admin.fedoraproject.org/mailman/listinfo/devel
