[ADVANCED] RMClock Powersaving, Whining Stop

[John Ratsey]

Very interesting, but I would prefer the theory to be backed up by some real life tests such as playing the same DVD under the same operating conditions except for changing the CPU options. DVD playback provides a partial CPU load so it should be a good indicator.

2W power consumption on C4 idle seems low to me. What is using the other 9W of the total 11W idle power consumption? Table 6 of the Intel data sheet 31674502 shows 9.4A current for ICC Intel Enhanced Deeper Sleep (top of 2nd page). The voltage range for this power condition is 0.55 to 0.75W. Leaving frequency and capacitance out and assuming watts - volts x amp then the power drain for IDC4 is between 5.17 and 7.05W. Does frequency / capacitance reduce this down to only 2W?

I'm also intrigued that you have a discharge monitoring options within the Performance Monitor. I've never found it on my computers.

John

[7oby]

Very interesting, but I would prefer the theory to be backed up by some real life tests such as playing the same DVD under the same operating conditions except for changing the CPU options. DVD playback provides a partial CPU load so it should be a good indicator.

I'm as well very interested in real life tests. I hope some guys do that an post their results.

I just added a new figure and document by intel which supports the thesis of getting work done quickly. Search for "admits" in my first posting.

Yesterday I did some testing with 720p movie trailers from apple. I tested three different voltages:

[ ] 1.1 GHz @11x SuperLFM 0.9V (= highest FID in SuperLFM for me)
[ ] 1.6 GHz @8x normal 0.9V (= highest FID in normal mode with lowest voltage)
[ ] 2.2 GHz @11x normal 1.0250V (= highest FID in normal mode)

In that particular case the 1.6 GHz option was the best. I played the content using coreavc. The OS did not choose the optimal GHz since it was too often in 2.2 GHz. Actually the OS/RMClock chooses based an CPU utilization and isn't aware of voltages.

In my second posting I just added a practical paper measuring power consumption if hardware acceleration is available (MPEG-2, VC-1, MPEG4-AVC). Search for "HW Accel". In that case hardware acceleration performs much better than any kind of software decoding. In the case of MPEG4-AVC you'll even hit 0-2% CPU utilization playing blurays.

2W power consumption on C4 idle seems low to me. What is using the other 9W of the total 11W idle power consumption? Table 6 of the Intel data sheet 31674502 shows 9.4A current for ICC Intel Enhanced Deeper Sleep (top of 2nd page). The voltage range for this power condition is 0.55 to 0.75W. Leaving frequency and capacitance out and assuming watts - volts x amp then the power drain for IDC4 is between 5.17 and 7.05W. Does frequency / capacitance reduce this down to only 2W?

I know the intel datasheets and since it's the same table that shows the TDP, I assume those 9.4A for Deeper Sleep are some worst case scenarios (also the 100°C Tjunction indicate that). Mybe during transition time Deeper Sleep -> break.

All other numbers I found are much lower:
http://www.lesswatts.org/documentati...n-power-mgmnt/
http://laptoplogic.com/resources/det...p?id=48&page=4

The other 9 Watt account for: memory (2GB), chipset (GM965), graphics core (X3100 in GM965 chipset), harddrive (it's spinning), w-lan, bluetooth, ...

I'm also intrigued that you have a discharge monitoring options within the Performance Monitor. I've never found it on my computers.

You have to be running on battery to have this one. Then under section battery there will show up an item Discharge rate.

My entire posting might be not valid for desktop computers: They have just C1, C2. Power saving isn't an issue for desktop computers that much anyway.

[Oppermann]

Nice post!
What settings do you suggest for a T9300 ?

something like this?:

11x SuperLFM
12x Normal
13x IDA

How about the C-states and should I enable the IDA under "advanced cpu settings"?

I find that when I use RMClock my system seems to be using more % of the cpu at idle, why is that ?

[flipfire]

wow this is getting pretty technical, so much for simplicity.

C4 Idle : 2 Watt CPU
1.4 GHz 100% Load = 14 Watt (these are undervolted numbers)
2.2 GHZ 100% Load = 20 Watt (these are undervolted numbers)

Playing video @2.2 GHz = 64% * 20 Watt + 36% * 2 Watt = 13,5 Watt

Im not quite sure i get your maths. Ill admit i skipped all this earlier.

Can you elaborate on this?

I thought we were using this formula:


-

For my stock T2500 its quite simple.

From wikipedia:



It uses 31watts of power at full throttle. Say i only need 1.4ghz of power:

1400mhz/64.5 = 21watts

Since you say full speed is better:

2000mhz/64.5 = 31watts

[7oby]

wow this is getting pretty technical, so much for simplicity.

I was hoping to find some guys who did some more investigation on this. It's not trivial and currently I don't think there is a trivial answer. Though this might change.

Can you elaborate on this?

I thought we were using this formula:

If you use that formula, you won't save energy by using a higher FID. Simply because the factor I'm earlier finished doing the task, the reciprocal of this factor I need more energy.

For reasons of simplicity let's assume those two:
C4 Idle : 0 Watt CPU
600 MHz : 10 Watt CPU

If I have the 600MHz clock running for 1 h, then I spend this amount of energy:

Energy_600MHz = 10 Watt * 1h = 10 Wh

According to the formula of intel, the power consumption of a 1200 Mhz clock must be 20 Watt. It's in 1/2h finished doing the task and will spend the remaining time in C4. It results in the same energy:

Energy_1200MHz = 20 Watt * 1/2h + 0 Watt * 1/2h = 10 Wh.

That's actually a corollary of the intel formula. As long as this formula holds, you won't save any energy ever by using a higher core clock.

I've put a graph underneath the three power measurements (probably after you read it). And the basic message is: This formula doesn't hold. The formula probably holds for any semiconductor including CPUs. But it doesn't hold for the power consumption of a notebook since there are more devices (memory, chipset, front side bus) drawing current which aren't included in this formula and those do have an impact. Those other devices depend on the processor state and are not constant. That's the deal.

For my stock T2500 its quite simple.
From wikipedia:

The intel datasheets mention the TDP (Thermal Design Power) as well as wikipedia does. That's a worst case scenario. And for practical reasons intel packages CPUs in classes of TDP. Therefore the T2600 CPU with 2.16 GHz has the same TDP as a T2400 with 1.83 GHz as shown on wikipedia.

However that's clearly not the case. A 1.83 GHz CPU consumes less power at full throttle than a 2.16 GHz CPU (given same production process, same batch, same stepping etc.). It's even a contradiction to intels own formula - see above.

Unfortunately TDP doesn't help here at all. Practical numbers help. Or something like
http://www.spec.org/power_ssj2008/

I've updated the first posting by a figure of intel that goes in this direction and is more advanced that this simple formula from the Core CPU marketing paper.

[flipfire]

If you use that formula, you won't save energy by using a higher FID. Simply because the factor I'm earlier finished doing the task, the reciprocal of this factor I need more energy.

For reasons of simplicity let's assume those two:
C4 Idle : 0 Watt CPU
600 MHz : 10 Watt CPU

If I have the 600MHz clock running for 1 h, then I spend this amount of energy:

Energy_600MHz = 10 Watt * 1h = 10 Wh

According to the formula of intel, the power consumption of a 1200 Mhz clock must be 20 Watt. It's in 1/2h finished doing the task and will spend the remaining time in C4. It results in the same energy:

Energy_1200MHz = 20 Watt * 1/2h + 0 Watt * 1/2h = 10 Wh.

Okay now im confused

Again, lets say we want to watch a 1 hour movie at 600mhz:

Energy_600MHz = 10 Watt * 1h = 10 Wh

Now lets watch a 1 hour movie in 1200mhz:

Energy_1200 = 20Watt * 1 hr = 20wh

Speedstep:
Running a processor at high clock speeds allows for better performance. However, when the same processor is run at a lower frequency, it generates less heat and consumes less power. In many cases, the core voltage can also be reduced, further reducing power consumption and heat generation. This can conserve battery power in notebooks, extend processor life, and reduce noise generated by variable-speed fans. By using SpeedStep, users can select the balance of power conservation and performance that best suits them, or even change the clock speed dynamically as the processor burden changes.

The power consumed by a CPU with a capacitance C, running at frequency f and voltage V is approximately[1]

P = CV2f.

For a given processor, C is a fixed value. However, V and f can vary considerably. For example, for a 1.6 GHz Pentium M, the clock frequency of can be stepped in 200 MHz increments over the range from 1.6 to 0.6 GHz. At the same time, voltage requirement decreases from 1.484 V to 0.956 V. The result is that the power consumption theoretically goes down with a factor 6.4.

[7oby]

Okay now im confused
P = CV2f.

Again, lets say we want to watch a 1 hour movie at 600mhz:

Energy_600MHz = 10 Watt * 1h = 10 Wh

Now lets watch a 1 hour movie in 1200mhz:

Energy_1200 = 20Watt * 1 hr = 20wh

The above formula doesn't account for idle states. Any Idle state C1, C2, C3 stops the entire execution pipeline and beginning with C2 core clock goes to zero. The first calculation that I've done in my fist posting does consider this fact and assumed a 100% CPU load in the 600MHz case and a 50% load in the 1200MHz case. If you want to say so, read the intel formula like this:

P = (% spend in C0-State) * Capacity * VCore^2 * f + (1 - % spend in C0-State) * Power in C4

It makes the formula somewhat better, but not too much.

Maybe you're saying it won't spend time in higher C-States if you play movies. Playing 720p content in Linux and using powertop I showed that it's still spending time in C3 (my Linux distro can't do C4 or isn't aware of that):



The average time spend in C3 each time it entered it was 1ms. On an 2.2GHz CPU that's 2200 clock cycles, where entire execution came to a stop.

--

I'm currently working on making things more clear and providing more practical experiments. But it's not finished. However for those, who follow this is the intermediate status:



The dark blue line are real measurements of power I've taken on my system at load. The higher the clock goes the more work the system is able to perform. If the system is not under full load, it stays the time that it's doing nothing in some idle state. Actually the 0 Mhz clock in the graph corresponds to the idle power consumption I measured on my system.

If the load is sufficiently small (like office work) I can choose whether the system should do this work at 600MHz or at 2.2 GHz.

Each task will be completed much faster and more time spend in C-States. The proportion by which tasks are performed faster has to make up for the additional power that's necessary during that time. If you take a pencil and a paper and work with either of the above two formulas (intel's or the extended one), you'll figure out that this can never happen. You could never make up for the additional power you require. Maybe I'll post the maths here, but it's useless anyway. It's useless because the measurements I've taken differ from this logical model.

I'll post the conclusions first and give explanations in a later posting:

. if there's a dot above the yellow line that means this VID/FID performs worse regarding energy that it would have been at 2.2GHz and spending more time in C-States. That is even true for the 600 Mhz SuperLFM mode.
. the best mode I found is the 1.6 GHz 0.9V mode, which beats any other below that frequency.

[UltiCOW]

This is one of the best posts I read in a long time!
Im relatively new to undervolting (just got my laptop last week) but have done lots of reading and getting into it for a while now.

I read this theory that you go by a few months ago in a german forum..they seem to compliment eachother very well

Thanks a lot for all of this!

-COW

PS: just running an orthos test, T8300: 12x @ 0.9750, been going stable for 3 hours now! I seem to be quite lucky

If you need some specific help/tests run from this machine let me know exactly what you need and maybe I can help. I want to help but Im just not really sure how to...

[UltiCOW]

Ahh Silly me,

I jsut realised you were the author of the German posts
You seem to get around

Respect!

-COW

[anpe008]

7opy:

First of all thanks the guide. Helped me a lot. Actually really a lot.
I have both Vista and XP. When I used Vista I noticed the bug 3 "VID/FID jumps" and I solved it by following your link above.

But I had this "jump" for XP as well. I have the same intel cpu like yours and use only 2 FID/VID as well (Super LFM: x11/0.9 and 11*1.0250). Using Orthos, TAT the voltage level showed the correct numbers, but when I defraged the system and checkd the monitor tab in RMclock sometimes the VID went up to 1.25...

Any idea to solve it?

Thanks again.