Why disabling cores does not reduce power consumption?

[voodooFX]

SuperMicro X8DTE-F + 1x Xeon E5620
4x WD RE4 1TB
2x Toshiba 500GB 2.5" 7200rpm
2x intel SSD 730 480GB
1x Mellanox ConnectX2
1x Adaptec 5405
1x LSI 9420

CPU with all 4 cores active, turbo active and hyperthreading active
IDLE = 121W

CPU with 2 cores active, turbo off and hyperthreading off
IDLE = 120W

not exactly what I was expecting -_-

 

[BlueLineSwinger]

Modern Intel CPUs automatically throttle down clock speeds and essentially shut down unused cores when the system is idle. Manually disabling the features you did really isn't going to help any.

 

[PigLover]

+1 to @BlueLineSwinger. Westmere and later CPUs are pretty good at getting to low power idle states and will turn down threads and "park" cores to minimize idle usage. Intel really got serious about idle power usage in the last few years and each generation (Sandy Bridge, Ivy Bridge and Haswell) get continuously better at it.

You'd see some difference from disabling the cores at load. You would probably see 20-30 watts difference under full load (e.g., while running a good synthetic test to maximize core utilization is Prime9).

Actually, getting 121w idle with the configuration you listed is pretty good. You've got a lot of power consumers listed besides the CPU. Back of the envelope they probably add up to at least 80-90w idle, meaning you are seeing 30-40w on the CPU. This is not too bad for a Westmere-class CPU.

SuperMicro X8DTE-F (at least 20w idle - 17w idle just for the 5520 chipset)
+ 1x Xeon E5620 (varies)
4x WD RE4 1TB (assuming they are spinning about 7w each for 28w)
2x intel SSD 730 480GB (negligible)
1x Mellanox ConnectX2 (about 11w idle)
1x Adaptec 5405 (about 7-9w idle)
1x LSI 9420 (about 14w idle)

 

[voodooFX]

Interesting, I was pretty sure to gain at least 10-20 watts.
The system with just the CPU and the RAM, with ubuntu loaded in RAM via USB key boot draws about 60w.

I guess you are right and I should be happy with the result I have. Maybe I could look for a L serie Westmere ..

Thanks

 

[PigLover]

Again - add up the piece parts of your power consumption. The CPU is likely not the culprit - and the L-series Xeon's idle power isn't that much lower than the others. L-series wins at load.

 

[bds1904]

Only thing left that would change anything is changing psu's, and that's only if your curent one isn't efficient. Changing from a 80+ to a 80+ gold could yield a 10w-20 reduction in power draw, especially if you severely oversized your current power supply.

Power supplies are very inefficient when run with less than 20% load. An 80+ power supply can be as low as 70% efficient under 20% power load. That's the reason the standards for "efficient" power supplies starts at 20% load.

You really shouldn't have ananything bigger than a 400w power supply right now.