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Old 2020-03-18, 22:31   #1
mrk74
 
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Default High CPU usage

I know Prime95 uses a lot of CPU but should it really be at 100% with no other browsers or anything else running? Is it ok to just let it go at 100%?



Related: I think I've read there is a way to lessen the load but I wouldn't have a clue how to do that, assuming I read correctly that there is a way.
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Old 2020-03-18, 22:34   #2
Uncwilly
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100% is normally desirable, if your machine can stay cool.

Look for throttle in the documentation (undoc.txt)
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Old 2020-03-18, 23:45   #3
phillipsjk
 
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If you have a multi-core CPU you can tell the software to only use less that all of them. This may make your productivity software more responsive.


The effect may be larger on CPUs without a unified cache. I got a big web-browsing speed up by telling mprime to stay away from one of my 4 L2 caches (by using only 6 of 8 cores, and using processor affinity).


Edit: Normally, prime95 is supposed to jump out of the way when you want to use the CPU. In practice, the cache gets evicted, limiting you to memory bandwidth and latency.

Last fiddled with by phillipsjk on 2020-03-18 at 23:49
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Old 2020-03-19, 00:25   #4
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Quote:
Originally Posted by mrk74 View Post
I know Prime95 uses a lot of CPU but should it really be at 100% with no other browsers or anything else running? Is it ok to just let it go at 100%?
If you're running it on a laptop, the answer depends heavily on the design of the laptop's cooling system. This is generally not a great idea, but well-designed laptops can handle it just fine.

If a desktop has problems with the heat generated, it is likely time to clean the dust out of the case. Some really cheap desktops may lack enough air movement to sufficiently cool the CPU @100%; adding a case fan (one determines size by measuring the spot where a case fan spot lacks its fan) can resolve this airflow problem. An all-in-one (like those machines built in to a desktop monitor) may have neither the chance to add a fan nor enough cooling for the CPU @100%; one discovers this by experiencing occasional crashes while P95 runs, or by noticing substantial changes in responsiveness while running other tasks.

I've never seen web browsing slow due to using all hyperthreads for P95-type processes on a desktop, but I'm also not very picky about responsiveness. I run my CPUs at 100% for years on end, and wouldn't imagine doing it any other way.
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Old 2020-03-19, 02:08   #5
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Quote:
Originally Posted by mrk74 View Post
I know Prime95 uses a lot of CPU but should it really be at 100% with no other browsers or anything else running? Is it ok to just let it go at 100%?

Related: I think I've read there is a way to lessen the load but I wouldn't have a clue how to do that, assuming I read correctly that there is a way.
Using the throttle directive as uncwilly suggested is one way. Reducing the number of cores in use by prime95 is another. Lowering the clock rate is another.

My guess is that cutting back on cores may not cost as much performance as the other approaches. While I've used throttle for years on a system whose cpu still seems fine, I wonder what the frequent thermal cycling it does means for reducing processor life.
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Old 2020-03-19, 02:46   #6
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I agree that throttling has questionable aspects. Constant expand-contract cycles could affect multiple aspects of the CPU internally, and its thermal interface. The real question is indeed temperature. If your CPU core readings are reported below 70 C in a program like HWINFO, you should not have problems. If the temps are up in the 70s, taking 1 core off from Prime95 would bring them back down. You should check your temps under load in any case. HWINFO is very informative and frequently updated to accommodate newer hardware.
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Old 2020-03-21, 14:26   #7
mrk74
 
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This is what I have.
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Old 2020-03-21, 14:35   #8
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Why would it be less than 100%? You want it to do work, so it does work on the cores you give to it.
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Old 2020-03-21, 15:01   #9
mrk74
 
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Quote:
Originally Posted by kuratkull View Post
Why would it be less than 100%? You want it to do work, so it does work on the cores you give to it.

My understanding of the technical side of computers is quite limited. My understanding is/was 100% was "maxed out" and you wouldn't/couldn't use it for too much else if it was already at 100%.
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Old 2020-03-21, 15:21   #10
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Quote:
Originally Posted by mrk74 View Post
My understanding is/was 100% was "maxed out"
Sure. 100% is maxed out. That's the point of applications like P95 - take advantage of all spare cycles that would otherwise have been wasted and do some useful computations.
Quote:
Originally Posted by mrk74 View Post
and you wouldn't/couldn't use it for too much else if it was already at 100%.
Depends. If the application that is using 100% is a "high priority" task, then all the lower priority ones have to wait around. However, P95 registers itself as a low priority (the lowest priority, in fact), and so all normal applications can work without much issue. P95 will yield (or rather, the Operating System will make it yield) to everything else as needed.

Have you noticed any difficulty in running any other application or general usage of the system?
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Old 2020-03-21, 15:24   #11
mrk74
 
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Quote:
Originally Posted by kladner View Post
I agree that throttling has questionable aspects. Constant expand-contract cycles could affect multiple aspects of the CPU internally, and its thermal interface. The real question is indeed temperature. If your CPU core readings are reported below 70 C in a program like HWINFO, you should not have problems. If the temps are up in the 70s, taking 1 core off from Prime95 would bring them back down. You should check your temps under load in any case. HWINFO is very informative and frequently updated to accommodate newer hardware.

I use CPUID. I have seen temps in the low 80's at times.
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