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What should the CPU usage be of a fully-loaded CPU that has been throttled?

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Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#91

Post by rahimiali »

RandomBK wrote: post #82

Another approach may be to take inspiration from the `cpu load` metric on *nix systems and go _above_ 100%. In this example, the CPU usage would be `200%`: The system would like to be doing twice as much as it's currently doing, but something's throttling it. Of course, this opens up other issues with how to aggregate multiple cores, what the benchmark for 'max' should be, etc. Perhaps the more fundamental answer is…

You might be thinking of the load average, not the cpu consumption of a particular process as reported, by, say, top or ps. The article is about the latter kind of tool.

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#92

Post by pabs3 »

foobar33333 wrote: post #69
wmf wrote: post #19

Power saving and "throttling" (usually it's un-turboing) are different cases that shouldn't be conflated; in one case the processor could run faster but in the other it can't. Ultimately we may want different metrics depending on what they're going to be used for. If you calculate relative to base frequency you will get utilization over 100% which is going to confuse some people. Linux has done some work in this area…

MacOS has a weird solution to throttling. They put a fake process in the process list which looks like it consuming x% of the resources but really it is just blocking some usage to allow the CPU to cool.

Linux has the same solution on my machine.

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#94

Post by waterhouse »

tayo42 wrote: post #74
foobar33333 wrote: post #68

Earlier quoted context omitted.

CPU usage is an incredibly complex metric that doesn't really explain what is actually going on. I noticed while running a benchmark I can get my CPU to 50c and 100% usage and it stays steady like that. But then I tried prime95 and my cpu very quickly hit 99c also at 100%. Likely the different benchmarks were both running as fast as they can but the prime95 one ran on a faster part of the cpu which could generate mor…

i think you could prove that on linux by getting the number of instructions run. I think perf has a way of getting that info for you. not sure if windows has something simmilar

Hmm, different workloads will have different mixes of instructions, which will take very different amounts of time per instruction (e.g. a chain of uncached memory lookups vs a tight loop of register-register arithmetic). If you had two instances of the same workload, and one was throttled, then yes, you could compare instructions per unit time. But comparing prime95 vs the other benchmark is likely misleading.

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#95

Post by Godel_unicode »

foobar33333 wrote: post #68
magila wrote: post #11

A key problem with this proposal is that modern CPUs do not have a single definitive maximum frequency. You have the base frequency which is rarely relevant outside of synthetic workloads then you have a variety of turbo frequencies which interact in complex ways. AMD's latest CPUs don't even have clear upper bounds on their frequency scaling logic. It's a big black box and the results can vary depending on the workl…

CPU usage is an incredibly complex metric that doesn't really explain what is actually going on. I noticed while running a benchmark I can get my CPU to 50c and 100% usage and it stays steady like that. But then I tried prime95 and my cpu very quickly hit 99c also at 100%. Likely the different benchmarks were both running as fast as they can but the prime95 one ran on a faster part of the cpu which could generate mor…

Sounds like you're actually comparing your CPU in avx mode vs not. This is a common source of this type of behavior, avx is insanely power hungry.

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#96

Post by Godel_unicode »

bigiain wrote: post #87
phire wrote: post #71

Earlier quoted context omitted.

By this proposal's logic, it would make total sense for processes on a boosting CPU core to report more than 100% cpu usage.

“Military power “ seems to fit perfectly… > The etiology of military power is from War Emergency Power (WEP) which in the WWII era was a higher than normal rating power (i.e. >100% rated power) setting on an aircraft engine. Such power settings were approved for short durations (typically 5 minutes or less) such as takeoff and battle maneuvers. > The term was quickly shortened to military power.

Please let's not add yet more military fetishizing to IT. "Military power" should refer to things like military engines, not totally unrelated electronic performance boost modes.

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#97

Post by sfisthemoon »

pabs3 wrote: post #93
sfisthemoon wrote: post #88

I’d love to see how many watts my process is using. After all, energy is the resource each thread is really consuming.

On Linux there is powertop for that: https://01.org/powertop/

Mac and Windows have something similar, though not as specific. They all appear to be rough estimates based on the CPU time and the frequency at the time the process ran.

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#98

Post by deviledeggs »

Godel_unicode wrote: post #96
bigiain wrote: post #87

Earlier quoted context omitted.

“Military power “ seems to fit perfectly… > The etiology of military power is from War Emergency Power (WEP) which in the WWII era was a higher than normal rating power (i.e. >100% rated power) setting on an aircraft engine. Such power settings were approved for short durations (typically 5 minutes or less) such as takeoff and battle maneuvers. > The term was quickly shortened to military power.

Please let's not add yet more military fetishizing to IT. "Military power" should refer to things like military engines, not totally unrelated electronic performance boost modes.

IT overlap is mostly because computers and the internet are military technology. Mainframes, IC's and the transistor itself were bankrolled by US military money.

The internet and GPS, the core technologies of our time, are both direct descendants of the US military.

You may not like it, but the entire IT and tech field are built on US military tech

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#99

Post by Godel_unicode »

dataflow wrote: post #65
gruez wrote: post #61

Earlier quoted context omitted.

>Utilization should be relative to the maximum frequency the CPU could be running the same instructions at How do you define "maximum frequency"? For desktops it's relatively easy to define since they usually have good cooling and power delivery that they can always hit the top frequency, but for laptops this often doesn't apply. It might be only able to sustain top frequency for less than a minute before thermal thr…

Whatever frequency it could execute the next cycle at, assuming there was no desire to minimize power usage. It's a transient measure, not a steady-state measure.

The manufacturer doesn't know this, nor is it easy to determine. Is the max turbo frequency on air the max? On water (if so with what size rad with which fans)? At what ambient temperature? Is the max including tau, if so does that max change when it's about to expire? What about if the CPU was on ln² but the user has run out and can't add more to the cooling pot?

Every one of those numbers is different, and frequently the only way to determine if a frequency is possible to use for stable operations is to try it and see.

Re: What should the CPU usage be of a fully-loaded CPU that has been throttled?

#100

Post by Godel_unicode »

dataflow wrote: post #83
gruez wrote: post #80

Earlier quoted context omitted.

At 5% load, you might think there's 95% capacity to spare, but really it's actually something closer to 65%.

3.5 GHz instead of 4.1 GHz is a 15% difference, not 30%. I never expect multicore performance to be the same as single-core so if that's what you're assuming, it's an unreal assumption. I expect lower clock speeds for multicore regardless of what Task Manager shows. But okay, so there's some discrepancy, whether 15% or 30%. Okay, so I might underestimate it, and... then what? What would actually go wrong? I think wha…

It sounds like you don't ever engage in capacity planning. You should read about it, real usage numbers are very important.
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