`On Sat, Feb 25, 2006 at, Dominik Brodowski wrote:> On Sat, Feb 25, 2006 at 01:53:26PM +0100, Adrian Bunk wrote:> > > > Doesn't less heat imply less power consumption?> > > > > > Not in this case no.> > >...> > > > Sorry for the dumb question, but how could this work physically?> > > > If a computer produces less heat with the same power consumption, what > > happens with the other energy?> > No. Let's do the math (again), and (again) for the actual values of an Intel> Pentium(R) M Processor, 1400 MHz @ 1.484 V, even though the same rules of> physics, logic and mathematics apply to _all_ processors.Do you have the numbers for a Pentium(R) 4 HT? (I couldn't findanything substantial with google.) Especially C2 vs. C2 + throttling?Because the way I remember having read somewhere, the idle(C2) power consumption of the P4 is significantly higherthan with the Pentium(R) M.> Power consumption in idle state C2 (Stop-Grant state)	 7.3 W> Power consumption when "skipping instructions"> 	because of throttling (Stop-Grant state)	 7.3 W> > Power consumption when doing work			22.0 W> > > This means that if the processor idle percentage is _larger_ than (1 -> throttling rate), throttling has no effect at all.On a Pentium(R) M, but how about P4? The two have very differentarchitectures, don't they?> Now, let's assume there is some work for the CPU to do which keeps it busy> for one second @ 1.4 GHz. How much energy is needed to get this work done?> > 0% throttling:		22 Ws	(1s)> 25% throttling:		24 Ws	(1.3s)> 50% throttling:		29 Ws	(2s)> 75% throttling:		44 Ws	(4s)> > > Now let's also assume there is nothing else to do during a span of four> seconds: then, independent of the throttling setting, the CPU power> consumption is 44 Ws for these four seconds.> > > However: for the 75% throttling state, the CPU only produces 11 W of heat> _all the time_ -- this means, the fan or air conditioning must only consider> 11 W. For 0%, the CPU may produce 44 W of heat in a second -- and to cool> that sufficiently, the fan _may_ need to run faster, which consumes more> energy than is saved by only having to cool 7.3 W (instead of 11W) the other> three seconds.This is all fine, but why would anyone use throttling when theCPU has work to do (except for thermal emergency throttling)?> So: P4-clockmod style throttling only makes sense if either> > a) the idle handler does not enter the Stop-Grant state (C2) efficiently, or> > b) the load varies significantly over time in a manner which has effect on>    the fan, and where the latency induced by throttling doesn't matter.Maybe my previous mails were not clear enough: The goal is toreduce idle power consumption (and by that fan noise). The PCis running but is idle, e.g just listening for possible incomingjabber messages or whatever.When I experimented with P4-clockmod some time ago, I observedthat the fan noise was reduced when I left the box run idlewith clockmod set to maximum throttling. I thought this wasa good thing.Anyway, 2.6.16-rc4 p4-clockmod driver doesn't work with my CPUanymore (booted with cpufreq.debug=7):CPU: Intel(R) Pentium(R) 4 CPU 2.60GHz stepping 09Checking 'hlt' instruction... OK....cpufreq-core: trying to register driver p4-clockmodcpufreq-core: adding CPU 0p4-clockmod: has errata -- disabling frequencies lower than 2ghzspeedstep-lib: x86: f, model: 2speedstep-lib: ebx value is 9, x86_mask is 9speedstep-lib: P4 - MSR_EBC_FREQUENCY_ID: 0xd12000d 0x0speedstep-lib: P4 - FSB 200000 kHz; Multiplier 13; Speed 2600000 kHzfreq-table: setting show_table for cpu 0 to b04be620freq-table: table entry 0 is invalid, skippingfreq-table: table entry 1 is invalid, skippingfreq-table: table entry 2 is invalid, skippingfreq-table: table entry 3 is invalid, skippingfreq-table: table entry 4 is invalid, skippingfreq-table: table entry 5 is invalid, skippingfreq-table: table entry 6 is invalid, skippingfreq-table: table entry 7 is invalid, skippingfreq-table: table entry 8 is invalid, skippingcpufreq-core: initialization failedcpufreq-core: no CPU initialized for driver p4-clockmodcpufreq-core: unregistering CPU 0Johannes-To unsubscribe from this list: send the line "unsubscribe linux-kernel" inthe body of a message to majordomo@vger.kernel.orgMore majordomo info at  http://vger.kernel.org/majordomo-info.htmlPlease read the FAQ at  http://www.tux.org/lkml/`