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-   -   CPU Energy Efficiency for Prime95 (https://www.mersenneforum.org/showthread.php?t=24757)

VBCurtis 2019-09-09 01:47

[QUOTE=scan80269;525492]I suspect the i9-9900T with high speed DDR4 memory (e.g. 3600 dual rank) may be hard to beat in efficiency, since the TDP is only 35W, so CPUs with higher TDP will need to deliver several times the throughput to come out on top. For example, even with AVX512 and 6-channel memory, I doubt if a Xeon W-3175X platform can achieve >7.2X the throughput of what I posted for i9-9900T/DDR4-3600. Wouldn't mind being proven wrong, though.

Perhaps the way to compare is to simply take the iters/sec figure for leading edge exponents (5120K FFT??) divided by the CPU steady state package power, with optimized thread and worker counts for each CPU.[/QUOTE]
I don't see how it is useful to compare CPU power draw for efficiency, rather than wall-socket power draw. If my CPU draws double the power of your 9900 for 50% more production, I think my system is more efficient per watt of power used, because my wall-socket power drawn is less than 50% more than yours. If you think of efficiency as "lowest cost of electricity per LL test completed", then it's wall-socket wattage for sure.

nomead 2019-09-09 13:01

[QUOTE=hansl;525485]Wouldn't the 3000 series chips be bandwidth limited with only 2 memory channels?[/QUOTE]

And they are, if the FFT size is large enough so that the data doesn't fit inside the L3 cache. If it does fit, the bandwidth limit is significantly higher, probably what the Infinity Fabric can transfer (write at half the speed of reads) is the limiting factor. See [URL="https://www.mersenneforum.org/showpost.php?p=524000&postcount=103"]benchmarks[/URL] and [URL="https://www.mersenneforum.org/showpost.php?p=525003&postcount=110"]speculation[/URL] in the Zen 2 thread.

retina 2019-09-09 13:34

[QUOTE=scan80269;525492]Perhaps the way to compare is to simply take the iters/sec figure for leading edge exponents (5120K FFT??) divided by the CPU steady state package power, with optimized thread and worker counts for each CPU.[/QUOTE]There is more to a computer than just the CPU. You need to measure all the components. RAM, mobo, PSU, GPU, HDD/SSD, fans, display, etc. A CPU doesn't run with nothing connected.

Buy one of those power plug watt meters and use that figure as the basis for efficiency computations.

scan80269 2019-09-10 01:54

OK. I picked up several used Watts-Up Pro meters a couple of years ago, and can put them to good use measuring AC power of my systems running Prime95.

Since virtually all of my systems running Prime95 are headless, with no display, keyboard or mouse attached, that is the way I'll be measuring the system power with watt meters.

Questions. Will system power vary by the assigned exponents? Should I just take AC power readings while the systems are running their current assignments? Would it matter if the current assignment is LL-D or PRP? Or should I pause the assignments and launch a specific torture test? Most of my systems are presently running PRP on exponents in the 88 million range.

VBCurtis 2019-09-10 03:19

Try your various ideas, report whether outlet-wattage varies among any of those things. I doubt it, but I am prepared to be surprised.

hansl 2019-09-10 03:43

As I understand it, the smallest of the FFTs are allegedly the most tortuous, so I would expect them to draw a few more watts than larger ones.

ewmayer 2019-09-10 19:41

[QUOTE=hansl;525602]As I understand it, the smallest of the FFTs are allegedly the most tortuous, so I would expect them to draw a few more watts than larger ones.[/QUOTE]

Not necessarily - those small FFTs fit almost entirely in L1/2 caches, so tend to stress the CPU the most. Larger FFTs will spill into L3 and then into main memory, so may leave the CPU slightly less stressed but the overall system more stressed. Watts-at-wall will tell the tale.

scan80269 2019-09-22 01:36

Here are two of my systems running Prime95 with AC power consumption measured using Watts-Up Pro meters:

System #1
- Intel NUC8i7BEH
- Intel Core i7-8559U CPU (28W TDP)
- 16GB DDR4-2133 memory (2 x Samsung 8GB 2133 2Rx8 SODIMM, CL15, CR=1T)
- Samsung 850 PRO 256GB SATA SSD
- Akasa Turing fanless chassis

4 cores 1 worker
PRP exponent 86831357, FFT=4608K
ms/iter: 5.736
AC power: 47.2W

System #2
- ASRock Z390M-ITX/ac motherboard
- Intel Core i9-9900T CPU (35W TDP)
- Nofan CR-95C passive heatsink (black pearl)
- 32GB DDR4-3600 memory (2 x Corsair 16GB 3600 2Rx8 UDIMM, CL17, CR=2T)
- Samsung SM961 512GB NVMe PCIe SSD
- Seasonic Prime Titanium 600W fanless power supply
- ThermalTake Core P1 chassis

8 cores 1 worker
PRP exponent 86846297, FFT=4608K
ms/iter: 4.513
AC power: 59.6W

Both systems are running headless: no display, keyboard or mouse attached.

The second system draws more power from the wall than the first system, but cranks faster. Efficiency wise (iters/watt) they are quite similar.

petrw1 2019-09-24 05:34

Power bill becoming a concern
 
I'm thinking of replacing some outdated CPUs for MUCH MUCH faster but hopefully NOT a lot more power consumption.

What would I need to buy to produce the same LL or P1 throughput as these 4 CPUs:
i5-2500
i5-3570
i5-3570
i5-3570K

For example my i7-7820X produces about the same P1 throughput as the first 3 combined
… at I suspect about 1.5 times the power draw of 1 of them.

The first PC above also has a GTX-980 GPU which I'd like to replace with maybe a 2080.

OR....might I be better off by rather than getting a big honking CPU to get a GPU that is efficient at P1/LL?

I understand Titan for example is really good at LL but not so great at TF whereas the 2080 is great at TF but so so at LL.

Is there a card that is good at both? (That doesn't cost the same as a car?)

scan80269 2019-09-24 06:51

[QUOTE=petrw1;526456]I'm thinking of replacing some outdated CPUs for MUCH MUCH faster but hopefully NOT a lot more power consumption.

What would I need to buy to produce the same LL or P1 throughput as these 4 CPUs:
i5-2500
i5-3570
i5-3570
i5-3570K

For example my i7-7820X produces about the same P1 throughput as the first 3 combined
… at I suspect about 1.5 times the power draw of 1 of them.

The first PC above also has a GTX-980 GPU which I'd like to replace with maybe a 2080.

OR....might I be better off by rather than getting a big honking CPU to get a GPU that is efficient at P1/LL?

I understand Titan for example is really good at LL but not so great at TF whereas the 2080 is great at TF but so so at LL.

Is there a card that is good at both? (That doesn't cost the same as a car?)[/QUOTE]

Recent generations of Intel desktop processors (e.g. Coffee Lake-R) should provide significant performance increases AND power reductions compared to your Intel 2nd gen Core (Sandy Bridge) and 3rd gen Core (Ivy Bridge) processors.

I've been a fan of low power Intel desktop processors, and am especially partial to the 35W series, such as i7-7700T (4-core, Kaby Lake), i7-8700T (6-core, Coffee Lake) and even i9-9900T (8-core, Coffee Lake refresh). These are paired with dual-channel DDR4 memory at 2400 or 2666, which has nearly twice the clock frequency of DDR3 memory at 1333 or 1600, or more than twice if you count memory overclocking. I've recently found DDR4-3600 dual-ranked (16GB sticks) memory quite optimal for running Prime95 PRP with leading edge exponents (FFT=4608K or higher).

My fastest system for Prime95 has a i7-5960X CPU (Haswell E, 140W) with quad channel DDR4-2133 CL14 memory, but its energy efficiency is substantially inferior to my i7-8559U and i9-9900T systems.

So it comes down to whether you want to pursue high energy efficiency or high absolute performance. Favoring the former can help lower your electric bill and still achieve some increase in prime computing throughput. The latter may get you to speed record territory but with a sizable penalty in electricity cost.

preda 2019-09-24 11:08

[QUOTE=petrw1;526456]I'm thinking of replacing some outdated CPUs for MUCH MUCH faster but hopefully NOT a lot more power consumption.
[...]
OR....might I be better off by rather than getting a big honking CPU to get a GPU that is efficient at P1/LL?

I understand Titan for example is really good at LL but not so great at TF whereas the 2080 is great at TF but so so at LL.

Is there a card that is good at both? (That doesn't cost the same as a car?)[/QUOTE]

Radeon VII is both powerful *and* efficient for PRP. (numbers: I run one of my RadeonVIIs in "power efficient" mode; it is using 150W (self-reported by the GPU; at the plug I measure about 25% more overhead), and does 955us/it at the wavefront)


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