Solved CPU vs Core(s)?

[markg2]

This may be somewhat far afield but--

I have a desktop gadget that measures CPU, Core and RAM % usage. It was my understanding that the CPU cores are the processing engines within the structure of the CPU. So I'm surprised to see that the Core 1 + Core 2 % at any given time is no where near the total value of CPU usage %.

I tried Googling and reading but I'm not finding this specific question/answer.

Even though this is not really directed at this forum's target, would someone mind offering up a quick explanation?

Thanks,

Mark

 

[mickey megabyte]

can you give us an example of your readings?

imagine a dual-core processor, and core 1 is being used 60%, and core 2 is 40% - then the average use is 50% for the whole cpu.

does this make sense?

 

[markg2]

If the object were to determine the average usage, then yes.

However, if the object is to determine the total usage at the moment of the CPU then why wouldn't the answer be to add core 1 + core 2 and have that % be the same as the cpu usage %--which it never is according to my desktop gadget?

 

[badger906]

But then if both cores were at 50% the cpu readout would say 100%?
Which would be miss leading.



Sent from my BlackBerry 9900 using Tapatalk

 

[markg2]

Okay, then what is the relationship between total cpu usage and % core usage?

 

[DeaconFrost]

It sounds like you are wandering off on a topic that isn't going to be very beneficial. There's no real relationship between the two. If you consider a dual core CPU, you essentially have two "brains" to do the calculations. They are somewhat independent, in that the total usage doesn't need to always add to 100%. If you had a single core, it wouldn't be 100% all the time, either. If one core is working on a task at 30%, the other core could sit idle, or it could be working on a separate task at 30%, 45%, etc...whatever.

That's the entire point behind multiple core CPUs...is to divide the workload up.

 

[badger906]

If you want a rough idea of the "total" percentage open task manager then minimise it.

The graph that shows up in the task bar is accurate enough.

Sent from my BlackBerry 9900 using Tapatalk

 

[mickey megabyte]

Okay, then what is the relationship between total cpu usage and % core usage?

total cpu usage = average of individual core usage

as badger906 said above, if both cores of a dual-core cpu were running at 50%, total cpu usage is 50% too - the cpu still has capacity to do the same workload again.

also if core 1 was 100% and core 2 was 0%, then the total usage would be 50% too...same as 75/25, 60/40 etc etc

it might help if you imagined you had two factories with 100 people employed in each one.

in factory A, 60 people are working hard, whilst 40 are slacking off looking at facebook. in factory B, 40 are working, 60 are picking their nose. so out of the total workforce in both factories, only 50% are working.

 

[bartekxx12]

Total CPU Usage for dual cores = (Core 1 + Core 2 usage) Divided by 2

And for all CPU's = (Sum of Usage of all cores) Divided by number of cores

Correct me if I'm wrong just tried to work it out here, but there is your relationship...

 

[bartekxx12]

Well that seems to work...

Core 1 : 20%
Core 2 : 27%
Total CPU Usage : 20+26= 46 /2 = 23%

Example 2 :

Core 1 : 16%
Core 2 : 50%
Core 3 : 24%
Core 4 : 68%

Total CPU Usage = 16+50+24+68 = 158 / 4 = 39.5% so rounded 40%

Example 3 : (Simplified)

Core 1 : 24%

Total CPU Usage = 24 /1 = 24%

 

[Teerex]

It's basic math really. You have 8 liters of milk in 8 bottles/cores. You drink half of each bottle, how much do you have left? 4l, or 50%. You drink one bottle 100%, leave the rest alone. You have drunk 12,5%.

 

[markg2]

Thanks--

Understood but for one point.

I thought I'd read that software has to be written to address specific cores to take advantage of multi-core processing.

Does that then mean that a core processing imbalance (core 1=10% & core 2=80%) cannot be simply adjusted by the cpu, moving more processing to core 2 since the application(s) running determine which of the two cores are used?

Mark

 

[bartekxx12]

Thanks--

Understood but for one point.

I thought I'd read that software has to be written to address specific cores to take advantage of multi-core processing.

Does that then mean that a core processing imbalance (core 1=10% & core 2=80%) cannot be simply adjusted by the cpu, moving more processing to core 2 since the application(s) running determine which of the two cores are used?

Mark

Read my post, if one is 10% and one is 80%

Total CPU Usage = 80 + 10 = 90 / 2 (amount of cores) = 45%

and about the adjusting, well it is also spread amongst the cores in some way it's just that an app optimized for multiple cores will do a better job then the CPU trying to spread the work...

 

[Teerex]

Only older or poorly written code targets a specific core (usually Core 0). Windows and most modern software distribute threads between cores. They even move them from one to another.

One thing though is still strictly set to one core, and those are hardware calls which go to Core 0. I hear Ivy Bridge might change that.

 

[bartekxx12]

Only older or poorly written code targets a specific core (usually Core 0). Windows and most modern software distribute threads between cores. They even move them from one to another.

One thing though is still strictly set to one core, and those are hardware calls which go to Core 0. I hear Ivy Bridge might change that.

Yeah most programs will use 2 cores, I rarely see a frozen program only using 25% of the CPU in task manager, what I do often notice is since I have a quad core most programs when they freeze for whatever reason will have CPU usage at 50% so they are only using 2 cores, so Im guessing optimization for quad cores is not near as good as for dual yet...

 

[markg2]

Thanks gentlemen--

My question has been answered.

Mark

 

[Britton30]

It's the average CPU usage as Mickey said. If one core is 45% and the other is 60% you'd have 105% usage which is impossible to be above 100%. The total CPU use is misnamed, in the above case it would be shown as 53% due to rounding up by CPU gauges.In this snip, usage is shown as 16% with one core over 50% and one is at zero.