Can someone explain CPU utilization?

[kol12]

What exactly is CPU utilization? Is it the capacity of a CPU? With some of latest games out now having high CPU utilization and frequent spikes of 90-100% on i5 CPU's why do these games demand more CPU capacity? Does clock speed have any relation to utilization, ie: will a faster clock speed reduce a CPU from reaching high utilization so often?

 

[The Paladin]

short version :

CPU utilization is a key performance metric. It can be used to track CPU performance regressions or improvements, and is a useful datapoint for performance problem investigations. It is also fairly ubiquitous; it is reported in numerous places in the Windows family of operating systems, including Task Manager (taskmgr.exe), Resource Monitor (resmon.exe), and Performance Monitor (perfmon.exe).

complete version at https://blogs.technet.microsoft.com/winserverperformance/2009/08/06/interpreting-cpu-utilization-for-performance-analysis/

 

[harrysmellington]

Utilization is how much a CPU is being used, If it is at 100% then it cannot operate any faster/take on more tasks. You might see high utilization in games where large sections of the game are being loaded outside of player view like in GTA V or when calculating the positions of swarms of enemies like in Ashes of the Singularity.

In terms of clock speed, it is not always directly related to capacity however in the case of i5 vs i7 clock speed can directly relate. Since an i5 and i7 of the same generation are the same chip, if they have the same clock speeds they will perform exactly the same. This however will change if a game can use 8 threads which is something the i7 has over the i5. In this case you may see a drop in utilization in the i7.

In terms of comparing clocks over different generations or manufacturers, you will have a hard time. There are many factors that contribute to the total performance (or capacity however you want to call it).

In short, performance of the CPU will determine what utilization it gets in game, CPUs that perform better (either by higher clocks or with more usable cores) will have lower utilization.

 

[kol12]

@harrysmellington

Thanks that is helpful. So does that mean that a higher clock speed does affect the level of utilization? If the CPU is able to process the required tasks quickly enough that would lower the load/utilization right?

So Does 100% CPU usage mean that the CPU can't process the required tasks quickly enough, or that there is to just too much workload, or does that mean the same thing?

 

[gamerk316]

CPU utilization is a measure of how much of a CPUs resources are used over a period of time. Keep in mind it's not an instantaneous measurement.

Also keep in mind that CPU utilization is an average value across all CPU cores. For example, you could have 25% total utilization on a four core CPU where one core is pegged at 100% load, indicating a task (singlethread dominated in this case) is bottlenecked by the CPU.

 

[harrysmellington]

100% means that there can be no more instructions running on the CPU, there will be a waiting list for instructions past this point. This is why you get lag when the CPU goes over 100% utilization as you have to wait for the CPU to complete a task before the next can be loaded in.

The main thing that you have to understand is that CPUs that can perform better will require less utilization to get the same performance as lower performing CPUs (e.g faster CPU @ 80% = slower CPU @ 100%). As you may or may not know there are more factors in CPU performance than just clock speed. You should also know that an i5 is the same chip as an i7 but with some of the features disabled so you can compare their performance relative to each other from their clock speed.

Think of it like a cup of water with a hole on the bottom. You can fill that cup by pouring water. If you pour faster than water is leaving the hole, the cup will fill and will become full. Once full you'll have to wait a little then pour into the cup so you don't spill it. A faster CPU is like a cup with a larger hole. You can also imagine that each CPU thread is a cup such that an i5 has 4 cups and an i7 has 8. Just remember few games support 8 cups.

 

[kol12]

@harrysmellington

So the i7 has 8 cups but still has the same size hole as the i5. Could you liken the hole in the cup to the CPU clock speed? A faster clock speed = a larger hole?

So if a CPU is seeing a lot of 90-100% usage is it likely to benefit from more threads rather than more clock speed?

I'm not sure this one got answered, does core speed affect the amount or rate of utilization?

 

[harrysmellington]

@harrysmellington

So the i7 has 8 cups but still has the same size hole as the i5. Could you liken the hole in the cup to the CPU clock speed? A faster clock speed = a larger hole?

So if a CPU is seeing a lot of 90-100% usage is it likely to benefit from more threads rather than more clock speed?

I'm not sure this one got answered, does core speed affect the amount or rate of utilization?

Clock speed does not by itself determine utilization, overall CPU performance does. Comparing the i5 and i7 is a special case, this is because they are the same in every other way except for 1) stock clock speed and 2) number of cups. Most of the time clock speed alone is superficial in determining performance (and thus utilization). So no you can't say that a larger hole is a faster CPU clock.

 

[kol12]

Clock speed does not by itself determine utilization, overall CPU performance does. Comparing the i5 and i7 is a special case, this is because they are the same in every other way except for 1) stock clock speed and 2) number of cups. Most of the time clock speed alone is superficial in determining performance (and thus utilization). So no you can't say that a larger hole is a faster CPU clock.

So clock speed has no effect when utilization is high, and the only way to reduce it is by spreading the load to more cores/threads? In that case what does clock speed affect?

 

[harrysmellington]

increasing the performance of your CPU will reduce utilization within similar tasks.
Read: http://www.kitchentablecomputers.com/processor2.php
This explains the factors that contribute to CPU performance (i.e widens the hole in the cup/adds more cups). Most of the time you'll need to get a better CPU to increase performance but on some you can simply increase the clock speed.

 

[dontlistentome]

I think the point of view here is off, the CPU is the thing that is being used, it's not the thing doing the using.

So you run a game, the game is the thing doing the using, in this case it's using the CPU. The game will use up as much of the CPU as its design demands. If it is a new game designed to use a lot of CPU performance, it will keep loading the CPU until one of two things happens. One, it gets as much CPU performance as it needs, so it does not demand more. Or two, it reaches the maximum the CPU has to offer. So that's when lag happens, as the CPU needs time to catch up to the demands being placed it.

"ie: will a faster clock speed reduce a CPU from reaching high utilization so often?"

The clockspeed is only one possible way of determining CPU performance. Just as important is the software you are running. Not all software is equally demanding. A low clockspeed multi-thread CPU might perform excellently on software that uses those threads, while a very high clockspeed single core single thread CPU may perform poorly on that same software.

As far as reducing utilization, you do that by selecting the correct components for your needs. This is why people always ask "What games are you going to play?" when answering questions about GPU or CPU advice. There is no single CPU that is the 'best' since what's best for you might not be what's best for me. Once you identify what you'll do with it, then it's possible to choose what's best for that particular purpose.

 

[kol12]

@dontlistentome

Some good points there. Part of the reason of my thread is to better understand high utilization ie 90-100%. It seems clear at this point that if utilization is that high the software or game likely requires more room, be it cores or threads and that core speed is no longer the issue, right?

Exactly what effect is most noticeable then from clock speed or a higher clock speed than a slower clock speed if the application is demanding the most it can get?