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Re:ECC matters by bayindirh on Sunday January 03, 2021 @12:33PM (#25623251)
> I've never seen anyone shop a desktop CPU by TDP, rather than by performance and price.

That's me. When I start to plan for a new system, I select the processor first and read its thermal design guidelines (Intel used to have nice load vs. max temp graphs in their docs) and select every component around it for sustained max load.

This results in a more silent system for idle and peace of mind for loading it for extended duration.

Re:ECC matters by 411111111111111 on Sunday January 03, 2021 @12:38PM (#25623302)
That's not necessarily correct.

You can passively cool threadrippers if you underclock them enough and have good ventilation in case.

Re:ECC matters by bayindirh on Sunday January 03, 2021 @12:46PM (#25623360)
If my only interest would be ECC, I might do that but, I develop scientific software for research purposes. I need every bit of performance from my system.

In my case loading means maxing out all cores and extended period of time can be anything from five minutes to hours.

Re:ECC matters by mlyle on Sunday January 03, 2021 @12:57PM (#25623467)
The problem is-- you can't compare the TDP nor even the system cooling design guidelines between AMD and Intel.

Both are optimistic lies, but-- if you look at the documents it looks like currently AMD needs more cooling, but actually dissipates less power in most cases and definitely has higher performance/watt.

Re:ECC matters by bayindirh on Sunday January 03, 2021 @01:09PM (#25623579)
> The problem is-- you can't compare the TDP nor even the system cooling design guidelines between AMD and Intel.

Doesn't matter for me since I'm not interested in comparing them.

> Both are optimistic lies, but-- if you look at the documents it looks like currently AMD needs more cooling, but actually dissipates less power in most cases and definitely has higher performance/watt.

I'm aware of the situation, and I always inflate the numbers 10-15% to increase headroom in my systems. The code I'm running is not a most case code. A FPU heavy, "I will abuse all your cores and memory bandwidth" type, heavily optimized scientific software. I can sometimes hear that my system is swearing at me for repeatedly running for tests.

I don't like to add this paragraph but, I'm one of the administrators of one of the biggest HPC clusters in my country. I know how a system can surpass its TDP or how can CPU manufacturers skew this TDP numbers to fit in envelopes. We make these servers blow flames from their exhausts.

Re:ECC matters by ethanpil on Sunday January 03, 2021 @01:29PM (#25623759)
Built a NAS. My #1 concern for choosing CPU was TDP. This machine is on 24/7 and power use is a primary concern where I live because electricity is NOT cheap.
Re:ECC matters by mlyle on Sunday January 03, 2021 @01:38PM (#25623870)
This is a poor way to make the choice. TDP is supposed to specify the highest power you can get the processor to dissipate, not typical or idle use. And since different manufacturers specify TDP differently, you can't even compare the number.

Performance/watt metrics and idle consumption would have been a far better way to make this choice.

If you have a choice between A) something that can dissipate 65W peak for 100 units of performance, but would dissipate 4W average under your workload, and B) something that can dissipate 45W peak for 60 units of performance, but would dissipate 4.5W under your workload... I'm not sure why you'd ever pick B.

Re:ECC matters by mongol on Sunday January 03, 2021 @02:16PM (#25624225)
Is there a metric to look for to understand what power consumption is at "idle" or something close to that? That is what confuses me. I don't want to spend a lot of money on something that will be always on, and usually idling, and finding that its power usage is way higher than I thought. But perhaps there is a metric that tells that. I have not looked closely at it.

Also, even though the CPU may draw less, can still the power supply waste more, just because it is beefy? Comparing with a sports car, they have great performance, but also use more gas in ordinary traffic? Can a computer be compared with that?

Re:ECC matters by mlyle on Sunday January 03, 2021 @02:30PM (#25624380)
> Is there a metric to look for to understand what power consumption is at "idle" or something close to that? That is what confuses me. I don't want to spend a lot of money on something that will be always on, and usually idling, and finding that its power usage is way higher than I thought.

Community benchmarks, from Tom's Hardware, etc.

The vendor numbers are make believe-- you can't use them for power supply sizing or for thermal path sizing. If you look at the cited TDP numbers today-- it can be misleading-- e.g. often Intel 45W TDP parts use more power at peak than AMD 65W parts.

On modern systems, almost none of the idle consumption is the processor. The power supply's idle use and motherboard functions dominate.

> Also, even though the CPU may draw less, can still the power supply waste more, just because it is beefy?

Yes, having to select a larger power supply can result in more idle consumption, though this is more of a problem on the very low end.