Aren’t newer CPUs especially AMDs more energy efficient?

AnthonyMouse 3 days ago | parent | next [-]

Newer CPUs have significantly better performance per watt under load, essentially by being a lot faster while using a similar amount of power. Idle CPU power consumption hasn't changed much in 10+ years simply because by that point it was already a single digit number of watts.

The thing that matters more than the CPU for idle power consumption is how efficient the system's power supply is under light loads. The variance between them is large and newer power supplies aren't all inherently better at it.

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0manrho 2 days ago | parent [-]

Also worth noting, as this is a common point for the homelabbers out there, fans in surplus enterprise hardware can actually be a significant source of not just noise, but power usage, even at idle.

I remember back in the R710 days (circa 2008 and Nehalem/Westmere cpu's) that under like 30% cpu load, most of your power draw came from fans that you couldn't spin down below a certain threshold without an firmware/idrac script, as well as what you mentioned about those PSU's being optimized for high sustained loads and thus being inefficient at near idle and low usage.

IIRC System Idle power profile on those was only like 15% CPU (that's combined for both CPUs), with the rest being fans, ram and the various other vendor stuff (iDrac, PERC etc) and low-load PSU inefficiencies.

Newer hardware has gotten better, but servers are still generally engineered for above 50% sustained loads rather than under, and those fans still can easily pull a dozen plus watts even at very low usage each in those servers (of course, depends on exact model), so, point being, splitting hairs over a dozen watts or so between CPU's is a bit silly when your power floor from fans and PSU inefficiencies alone puts you at 80W+ draw anyway, not to mention the other components (NIC, Drives, Storage controller, OoB, RAM etc). Also, this is primarily relevant for surplus servers, but lot of people building systems at home for the usecase relevant to this discussion often turn to or are recommended these servers, so just wanted to add this food for thought.

	▲	AnthonyMouse 2 days ago \| parent [-]
		Yeah, the server vendors give negative fucks about idle power consumption. I have a ~10 year old enterprise desktop quad core with a full-system AC power consumption of 6 watts while powered on and idle. I've seen enterprise servers of a similar vintage -- from the same vendor -- draw 40 watts when they're off.

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0manrho 2 days ago | parent | prev [-]

If the point is a multi-tasking sandbox, not heavy/sustained data-crunching, those old CPU's w/ boosting turned off or a mild underclock/undervolt (or an L spec which comes iwth that out of the box) really aren't any more power hungry than a newer Ryzen unless you intend on running whatever you buy at high load for long times. Yeah, on paper it still could be a double digit percentage difference, but in reality we're talking a difference of 10W or 20W if you're not running stuff above 50% load for sustained periods.

Again, lots of variables there and it really depends on how heavily you intend to use/rely on that sandbox as to what's the better play. Regional pricing also comes into it.