5 ms·

> So where do I find the actual maximum power consumption on recent desktop CPUs then? Unfortunately you do this by putting it on a motherboard and and general

by leeter 6y ago

> So where do I find the actual maximum power consumption on recent desktop CPUs then? Unfortunately you do this by putting it on a motherboard and and generally putting an amp meter on the 12v EPS rail. Either that or just power from wall. The CPU vendors have worked really hard to hide this. Mostly because for most people it's largely irrelevant these days as the CPU will scale to cooling and power delivery. There are some limits though.

derefr 6y ago
You'd think "power consumption for prolonged 100% all-cores workload" would be the most relevant thing when selling server chips specifically, though, since it translates directly into OpEx. And yet even on those data sheets it's nowhere to be found.
- leeter 6y ago
  So for that it's "Easier" because you check the VRM spec for the socket for server. That's the maximum draw the manufacturer expects any CPU for that socket to ever pull. Then generally most of the higher end parts will vary clock speed vs cores etc to stay on that line. This works because server motherboard manufacturers only ever build to that spec and not one iota beyond it for cost reasons. But yeah... average expected draw is going to be interesting and most manufacturers won't give a number to avoid getting sued.
  - jandrese 6y ago
    Yeah, but the mobo manufacturer has to plan on you putting in the thirstiest chips on there, when you might be putting lower end chips on because your workload is mostly memory or PCI channel constrained and you are looking to max out the density in the rack. Of course you also have to consider the cooling capacity of your chassis. 170W in a 1U form factor needs a hell of a lot of airflow to avoid thermal throttling, especially on a dual CPU motherboard. Plus you gotta fit the power supply and everything else in there.
    - deusexepsilon 6y ago
      I really feel you have a whole team that can do that when you want and need it. In regards to the new 3DS XL, Â a little "un-cheating" because of a few bugs and an awning bugs, but a lot of them are not a problem. The biggest is that if you place the volume on the front of the motherboard, you're gonna have no problems. The only real issue is getting any of the parts on your board to work more in a PCI-accurate manner.
- 013a 6y ago
  Prolonged 100% all-core workloads, at what clock speed? With what cooling solution? All of these factors are variable. You could produce a number that says "the maximum clock the part is capable of, with a perfect cooling solution", but that number would never be reached in anything short of a liquid nitrogen testbench, and thus would be pointless outside of an academic setting. Intel was literally demonized for trying something similar to this two years ago, when they benchmarked a 28 core 5Ghz chip without disclosing that it was overclocked, and hooked up to an industrial water cooler [1]. In reality, this number can be found, but it would be an irrelevant number. [1] https://www.tomshardware.com/news/intel-28-core-cpu-5ghz,37244.html https://www.tomshardware.com/news/intel-28-core-cpu-5ghz,372...
- thawaway1837 6y ago
  If you’re selling server chips you’re likely selling to clients who are gonna do their own tests and trials under their use cases anyways. They aren’t even gonna look at numbers supplied by the manufacturer. And if you advertise power consumption for those kind of workloads (100% usage) to regular consumers, who are probably gonna buy 1 computer every 3-5 years, you’re disincentivized from optimizing the kind of stuff that have seen real gains, such as designs that aggressively and cheaply turn on/off systems, or clever decisions to run the chip slower than its max output to improve power consumption, without making an impact noticeable by a human user.
- kllrnohj 6y ago
  But what 100% workload? Is it 100% integer throughput? In which case it'll use a small fraction of the power of a blended integer & float workload. What about AVX-512? Is that considered 100% or beyond 100%? How much RAM is in play? Is it entirely an L1/L2 workload such that memory is never a bottleneck? Or is RAM used and then the CPU isn't really hitting maximum compute throughput? Or is it RAM reads & writes perfectly intermixed with integer & float computations that will always be L1/L2 cache hits, even though literally nothing will ever have that flawless of an execution in terms of power consumption? With how much of a CPU is dynamically gated & power controlled there is a difference between "maximum theoretical draw" and "maximum a 'real world' 100% load" will hit.
nottorp 6y ago
Yeah, it's irrelevant if you buy prebuilt. If you build it yourself, how do you know how to spec the system? You either waste resources by overspeccing it or you waste money by paying for something that can't run at full tilt on your system. And if you care about quiet and cool computing, you're screwed even more. A CPU that will run until it hits thermal limits means maxed out fan speed. I don't want maxed out fan speed. Are there any CPU coolers left that allow you to set a fixed speed manually? :)

by leeter 6y ago

derefr 6y ago

You'd think "power consumption for prolonged 100% all-cores workload" would be the most relevant thing when selling server chips specifically, though, since it translates directly into OpEx. And yet even on those data sheets it's nowhere to be found.

leeter 6y ago
So for that it's "Easier" because you check the VRM spec for the socket for server. That's the maximum draw the manufacturer expects any CPU for that socket to ever pull. Then generally most of the higher end parts will vary clock speed vs cores etc to stay on that line. This works because server motherboard manufacturers only ever build to that spec and not one iota beyond it for cost reasons. But yeah... average expected draw is going to be interesting and most manufacturers won't give a number to avoid getting sued.
- jandrese 6y ago
  Yeah, but the mobo manufacturer has to plan on you putting in the thirstiest chips on there, when you might be putting lower end chips on because your workload is mostly memory or PCI channel constrained and you are looking to max out the density in the rack. Of course you also have to consider the cooling capacity of your chassis. 170W in a 1U form factor needs a hell of a lot of airflow to avoid thermal throttling, especially on a dual CPU motherboard. Plus you gotta fit the power supply and everything else in there.
  - deusexepsilon 6y ago
    I really feel you have a whole team that can do that when you want and need it. In regards to the new 3DS XL, Â a little "un-cheating" because of a few bugs and an awning bugs, but a lot of them are not a problem. The biggest is that if you place the volume on the front of the motherboard, you're gonna have no problems. The only real issue is getting any of the parts on your board to work more in a PCI-accurate manner.
013a 6y ago
Prolonged 100% all-core workloads, at what clock speed? With what cooling solution? All of these factors are variable. You could produce a number that says "the maximum clock the part is capable of, with a perfect cooling solution", but that number would never be reached in anything short of a liquid nitrogen testbench, and thus would be pointless outside of an academic setting. Intel was literally demonized for trying something similar to this two years ago, when they benchmarked a 28 core 5Ghz chip without disclosing that it was overclocked, and hooked up to an industrial water cooler [1]. In reality, this number can be found, but it would be an irrelevant number. [1] https://www.tomshardware.com/news/intel-28-core-cpu-5ghz,37244.html https://www.tomshardware.com/news/intel-28-core-cpu-5ghz,372...
thawaway1837 6y ago
If you’re selling server chips you’re likely selling to clients who are gonna do their own tests and trials under their use cases anyways. They aren’t even gonna look at numbers supplied by the manufacturer. And if you advertise power consumption for those kind of workloads (100% usage) to regular consumers, who are probably gonna buy 1 computer every 3-5 years, you’re disincentivized from optimizing the kind of stuff that have seen real gains, such as designs that aggressively and cheaply turn on/off systems, or clever decisions to run the chip slower than its max output to improve power consumption, without making an impact noticeable by a human user.
kllrnohj 6y ago
But what 100% workload? Is it 100% integer throughput? In which case it'll use a small fraction of the power of a blended integer & float workload. What about AVX-512? Is that considered 100% or beyond 100%? How much RAM is in play? Is it entirely an L1/L2 workload such that memory is never a bottleneck? Or is RAM used and then the CPU isn't really hitting maximum compute throughput? Or is it RAM reads & writes perfectly intermixed with integer & float computations that will always be L1/L2 cache hits, even though literally nothing will ever have that flawless of an execution in terms of power consumption? With how much of a CPU is dynamically gated & power controlled there is a difference between "maximum theoretical draw" and "maximum a 'real world' 100% load" will hit.

nottorp 6y ago

Yeah, it's irrelevant if you buy prebuilt. If you build it yourself, how do you know how to spec the system? You either waste resources by overspeccing it or you waste money by paying for something that can't run at full tilt on your system. And if you care about quiet and cool computing, you're screwed even more. A CPU that will run until it hits thermal limits means maxed out fan speed. I don't want maxed out fan speed. Are there any CPU coolers left that allow you to set a fixed speed manually? :)