If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
On Tue, 12 Oct 2004 21:34:06 +1300, Michael Brown wrote:
keith wrote: alexi wrote: Michael Brown wrote: Nadeem wrote: rms wrote: http://techreport.com/ja.zz?comments=7417 The results sound awful. I wonder what they actually used to measure the wattage? Presumably one of the many household-appliance-power-meter things. There's a difference between running hot and being power hungry. The Prescott is both (ie: runs hotter and uses more power than the Northwood), but judging from these results the 90nm A64's are less power-hungry than the 130nm parts. The jury appears to still be out on whether it runs hotter or not. What really needs to be done is for someone (TectReport would be good, since they already have a 90nm 3500+) to test the chips at a large range of frequencies and plot the results. If the results look like (view with fixed width font): graph snipped Power consumption of CMOS is _proportional_ to core frequency. Therefore the chart is likely to be something like this: Not at *all* true. Active power consumption is proportional to frequency times voltage *squared*. You assume voltage is a constant; it's not. You also ignore leakage, which is an even higher-order issue, WRT voltage. We're not in the 20th century, Toto. If you've got a few minutes, Sure, that's why we're here, eh? ;-) there's a couple things I'd like clarification on ... My original graph was drawn on the basis that in modern CPUs, nothing is ever so nice as to go bad in only a linear way The more things stay the same... ;-) The only transistor physics I have done is for low frequency and theoretical transistors (and from a physics as opposed to engineering point of view) in which case the power usage is proportional to the switching frequency, all other things remaining equal. Assumimg also that modern CPUs are FET-like instead of bipolar. CMOS, certainly. There are few "passive" devices (like bipolar or N/PFET). ...at least not on purpose. The problem is in the details. What actually happens in the *real* world? Assuming voltage remains constant, how non-linear (with respect to frequency) is a transistor in the range that it's typically being pushed in a modern CPU? And what is the main contributor to that non-lineararity? The "real world" five years ago could be modeled quite like you propose. The power more-or-less proportional to the *active* CMOS power equations, much like; P ~ kCFV**2. Forgetting the "static" (or leakage) power, was easy since it wasn't a big issue (perhaps 10%). The world changed at 130nm and is getting worse exponentially as the structures shrink. (If you don't believe me look at the ratio of standby/active power of a PII vs. PIV at the same voltage.) Speed is still proportional to the voltage, but the power is proportional to (at least) the square of the voltage. What's changed is that the static (leakage) power is now a very significant part of the power budget. Since leakage isn't a resistive effect (current goes up at a higher rate than voltage) the power dissipated is even a higher-order function. Leakage sux! ;-) There are two major contributors to this power, sub-threshold leakage (essentially current through the ever-shortening channel when the device is "off"), and gate tunneling (current tunneling across the few-atom thick gate oxide). Both of these currents are a huge function of voltage. Both can be mitigated by a smart choice of devices and operating condiditons. A processor designed for a server may use lower threshold devices (that leak like hell) and very thin gate oxide (likewise). ...and pay for it in power dissipation. A laptop may make the oppposite choice. Indeed within a single system one can control the voltage (the only independent variable[*]) depending on the processing needs. [*] suspending clocks doesn't change the power for the work done, since 'f' is a linear function WRT power/performance. My issue here is that voltage is *not* a constant. Even the Pentiums had different voltage ratings across the product line. THe PII made it a function of the processsor module (but was still static). TMTA (I believe) introduced the concept of varying the voltage dependent on the processing needs. This is now a requirement. A single graph that shows power vs. frequency for a processor family doesn't show anything close to the whole picture. -- Keith |
#22
|
|||
|
|||
In comp.sys.ibm.pc.hardware.chips keith wrote:
My issue here is that voltage is *not* a constant. Even the Pentiums had different voltage ratings across the product line. THe PII made it a function of the processsor module (but was still static). TMTA (I believe) introduced the concept of varying the voltage dependent on the processing needs. This is now a requirement. A few more things. IIRC Tom Burd's PhD thesis was on the dynamic voltage variance. (The ex-Berkeley CPU infopad maintainer) AMD/Intel had to be more conservative in doing dynamic voltage supply because of more extensive use of custom/dynamic logic. Some of the non standard/non static CMOS stuff doesn't like to have the supply voltage change on them very much, but the pressure to reduce power is leading everyone down similar paths. Foxton is advertised as the enabling technology for Montecito. (dynamic frequency/voltage adjustment for power-performance optimization @ 90nm node) Without Foxton, Montecito would have ended up having to eat 3X of the power of Madison. (So sayth the "whitepaper") -- davewang202(at)yahoo(dot)com |
#23
|
|||
|
|||
"keith" wrote in message news On Tue, 12 Oct 2004 21:34:06 +1300, Michael Brown wrote: What actually happens in the *real* world? Assuming voltage remains constant, how non-linear (with respect to frequency) is a transistor in the range that it's typically being pushed in a modern CPU? And what is the main contributor to that non-lineararity? The "real world" five years ago could be modeled quite like you propose. The power more-or-less proportional to the *active* CMOS power equations, much like; P ~ kCFV**2. Forgetting the "static" (or leakage) power, was easy since it wasn't a big issue (perhaps 10%). The world changed at 130nm and is getting worse exponentially as the structures shrink. (If you don't believe me look at the ratio of standby/active power of a PII vs. PIV at the same voltage.) Speed is still proportional to the voltage, but the power is proportional to (at least) the square of the voltage. What's changed is that the static (leakage) power is now a very significant part of the power budget. Since leakage isn't a resistive effect (current goes up at a higher rate than voltage) the power dissipated is even a higher-order function. Leakage sux! ;-) There are two major contributors to this power, sub-threshold leakage (essentially current through the ever-shortening channel when the device is "off"), and gate tunneling (current tunneling across the few-atom thick gate oxide). Both of these currents are a huge function of voltage. Both can be mitigated by a smart choice of devices and operating condiditons. A processor designed for a server may use lower threshold devices (that leak like hell) and very thin gate oxide (likewise). ...and pay for it in power dissipation. A laptop may make the oppposite choice. Indeed within a single system one can control the voltage (the only independent variable[*]) depending on the processing needs. [*] suspending clocks doesn't change the power for the work done, since 'f' is a linear function WRT power/performance. My issue here is that voltage is *not* a constant. Even the Pentiums had different voltage ratings across the product line. THe PII made it a function of the processsor module (but was still static). TMTA (I believe) introduced the concept of varying the voltage dependent on the processing needs. This is now a requirement. A single graph that shows power vs. frequency for a processor family doesn't show anything close to the whole picture. -- Keith You are confused with a bunch of different concepts. Your first confusions is about "voltage" and "product line". Voltage is something engineers are using at will, to make the product work for it's targeted frequency but staying within reasonable reliability of devices and total power envelope. The voltage is a variable that you can control during your experiments with processor clocking and plotting charts of processor power versus core clock. If you want to compare two processors, one at 130nm, and another at 90nm, to see how their power grows with frequency, you run them at their corresponding _constant_ voltages (and temperatures), and you get the picture I charted before. Even if you are correct that "Pentiums had different voltage ratings across the product line", you still can run each processor at the same voltage while lowering core frequency down to get data points. Or increasing frequency, as all overclockers do, and they do change voltage at will. If you are trying to compare same (similar? if can find one!) processors on 0.35um, 0.25um, 0.18um, etc. process along the frequency axis, then this is a different story, the story called "CMOS scalability". Then yes, the classic CMOS scalability is severely broken starting from 0.25um, so the voltages between process generations are not going _down_ as they are expected from proportional geometry shrinks (because you can't shrink transistors proportionally any more because of various atomic-level limitations). I guess one can call it "non-linear" shrinks :-( The original question was, as I read it, "what is non-linear" with "transistors" as designs are pushed to higher frequencies (as the original chart clearly implies). The correct answer is that there is nothing really "non-linear" with CMOS transistor _GATES_. The whole known methodology of designing processors is still based on "flip-stay-flop" concept, therefore even today's processors still follow the basic power formula. A quick summary of CMOS power consumption basics can be found, e.g. he http://www.cse.psu.edu/~vijay/iscatu...al-sources.pdf Some (not very nice) discussion about common misconceptions about leakage, dynamic power, and heat sinks can be found at RWT: http://www.realworldtech.com/forums/...stNum=1224&Thr ead=1&entryID=14502&roomID=11 You can find there an example of how 0.13um Pentium-4 power scales with frequency, all based on published specification data for Icc. From these documents it is clear that I am the last person who should be accused of "forgetting leakage". What happens in "real world"? In high-performance processor world, very simple - you push your design to the limits dictated by throat-cutting competition, by tweaking geometry, process corners, voltage, leakage, making thermal slabs and heat-pipe based heat sinks, all for one reason - to maintain a foothold in market share. When you hit a wall, everything is very strongly non-linear - a brick wall :-) - aap |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Athlon64 Spanks P4 in 90nm Power Consumption tests | rms | Overclocking | 22 | October 13th 04 06:22 AM |
my new mobo o/c's great | rockerrock | Overclocking AMD Processors | 9 | June 30th 04 08:17 PM |
Happy Birthday America | SST | Overclocking | 333 | November 27th 03 07:54 PM |
Happy Birthday America | SST | Overclocking AMD Processors | 326 | November 27th 03 07:54 PM |
How can I make motherboard to restart after power loss automatically? | Amiran | General | 1 | September 24th 03 11:35 PM |