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

devblogs.microsoft.com

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

#111

Post by ithkuil »

deviledeggs wrote: post #98
Godel_unicode wrote: post #96

Earlier quoted context omitted.

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

Civilian and military engineering history are intertwined. The tech transfer doesn't go one way only.

In ancient times both mercantile and military incentives propelled the design of ships. Is fair to say the whole ship building field built on military tech?

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

#112

Post by ithkuil »

freeone3000 wrote: post #85
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.

This used to be the case -- XP era had it report as a percentage of the target frequency, so an Athlon XP would usually run at 110%. This is confusing to people who believe 100% is the maximum.

"these go to eleven!"

https://youtu.be/hW008FcKr3Q

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

#113

Post by waterhouse »

tayo42 wrote: post #106
waterhouse wrote: post #94

Earlier quoted context omitted.

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.

Yeah that would be the thing to prove that prime95 is going through more instructions so the cpu runs hotter

I see. But I expect that some instructions cost more (i.e. generate more heat) than others. Someone mentions AVX instructions, for example; presumably 1 million AVX-512 fused-multiply-add instructions cost a lot more than 1 million loads (we can probably arrange for the right proportion of loads to hit a CPU cache vs. go to main memory, so that they end up taking the same time). Even without AVX, I imagine things like 64-bit integer divisions or CRC32 instructions cost more than loads or stores, though I don't know by how much.

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

#114

Post by matco11 »

Perhaps, the system should report two numbers: the % usage of the CPU overall resources and the % usage of the throttled resources.

There is no constraint that one has to use only one number. Perhaps, in 2021, CPUs are complex enough to deserve more than one number to give a useful representation of utilization, as it works with all sorts of factories/plants. Also, who would love to see in the metrics reported CPU usage per core?

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

#115

Post by sharedfrog »

axaxs wrote: post #86
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…

Not following. Linux reports each core as 100%. So an 8 core machine maxes at 800%. So seeing 200 load doesn't indicate to me that it's throttled, but that it's using the equivalent of two full cores. Or did I misunderstand?

They're saying it can go over 1(00%) per core.

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

#116

Post by Const-me »

> “dynamic frequency scaling”, a feature that allows software to instruct the CPU to run at a lower speed, commonly known as “CPU throttling”

AFAIK that's not how it works in modern CPUs. Dynamic frequency scaling is a black box implemented in hardware. Software, and even OS kernels, have very little input over that. They can't subscribe for status updates. Even just getting the current frequency seems impossible, only indirectly by comparing RDTSC output (absolute time unscaled) with performance counters.

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

#118

Post by bserge »

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…

> my cpu very quickly hit 99c also at 100%

That should never happen and it's ridiculous that we just let manufacturers get way with it.

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

#119

Post by concerned_user »

CodeWriter23 wrote: post #117

I think this article asks the wrong question. The correct question IMO is why is the frequency throttled instead of maxed out when a program is saturating the CPU?

If it is thermal throttling then it means cpu is maxed out for the given conditions.

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

#120

Post by bserge »

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.

"Overdrive"
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