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why is maximum CPU utilization a major goal in design of scheduling algorithms?


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#1 radhika12

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Posted 18 January 2015 - 01:00 PM

I just wanted to ask that what is the reason behind making the maximum utilization of the processor ,that is ,whenever at any instant of time ,the scheduler makes sure that the processor must not remain idle and it must always be in the process of executing some process,so does that not require more power to be consumed by the processor.

So basically what is the reason behind always making the processor run,what would be the drawback if the processor remains idle,will that not save the power consumed by the processor.



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#2 PcPhoenix

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Posted 18 January 2015 - 01:10 PM

I don't believe there is a goal to ensure constant "maximum utilization" of the processor. When your system is doing some cpu-intensive work, your CPU activates higher power states which consume more power. When the CPU has less work, it drops down to lower power states which use less power.

Once your CPU is already in it's lowest power state, it doesn't really matter what it does at this point, it will consume the same amount of power. On most O/S's, there are usually idle tasks that are done while you are not using your computer which involves caching, paging, and other organization to maximize performance. All this work is done with lowest priority, so if you launch a task yourself it will always override the idle tasks.

 



#3 radhika12

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Posted 18 January 2015 - 01:28 PM

This is what I am not able to understand that if CPU is idle for some particular amount of time,then why does the OS tries to schedule more and more tasks to it ,so that it does not remain idle ,in which terms are we talking about " to maximize performance" ,and as far as I believe that the processor will consume same amount of power for execution of processes,the power consumed by different components which will be scheduled jobs by the CPU would be high .please correct me I said anything wrong.



#4 PcPhoenix

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Posted 18 January 2015 - 01:54 PM

This is what I am not able to understand that if CPU is idle for some particular amount of time,then why does the OS tries to schedule more and more tasks to it

 

Lets use defragging as an example. Over time, your hard disk becomes fragmented and different parts of data are saved in different parts of your hard drive platter. This is not optimal, and it slows down computer performance. So, a long time ago, people developed a process called "defragging", which organizes your hard drive and puts all the bits of data in the same area, so it can be read faster with less work for the drive. This "defragging" process takes lots of time.

So in modern OS's, when your computer detects that you are not using the computer (idle), it automatically begins defragging your disk in the background. This way, whenever you check your drive, it will always be organized. If you check on an older OS (Windows 95, 98 era), you will not see this effect.

There are many tasks like defragging that can be done by your computer while you're not using it. Most of these tasks are organizational in nature and involve sorting and organizing various things on your system to improve performance.

But, again, not all computers have to do this. You can configure windows to automatically hibernate/sleep or even shutdown if you haven't been using it for a long enough time.


Edited by PcPhoenix, 18 January 2015 - 02:10 PM.


#5 radhika12

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Posted 18 January 2015 - 02:41 PM

But if at some point of time ,if there is no need of defragmentation ,then won't that waste the power of CPU ,so basically I am unable to understand that why actually there is a need of always making the processor run ,if it remains idle will it waste power ,I guess ,no ,because ,the power consumed by the processor would always remain same whether it is executing one process or large number of processes.



#6 Datcoolguy

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Posted 20 January 2015 - 09:56 PM

The CPU will use more power when working at full capacity, but if you are asking why it never reaches down to 0 while the computer is on it's because there's always something in the background that needs it to work. It's not about always using the CPU, it's about doing the mundane tasks when the CPU isn't being used in order to avoid doing them when the CPU needs all of it's power to do something else. And quite frankly computer hardware doesn't actually consume that mutch power, especially CPU's when idling.

 

A big gaming super gaming rig will consume 1000 Watts tops, the same amount a common heater would. You know, just saying


"If you don't understand how your computer works, you shouldn't be messing with it!"


#7 Nikhil_CV

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Posted 30 January 2015 - 11:47 PM

If the processor is in the state of not doing any work, it will consume the lowest amount of power.
But cutting the power to processor while it has no work to do (as per user's view) will clear off the Cache contents and crash your machine / increase the latency to a very high time frame.
Idling is like you were reading a novel, after few chapters you kept opened the book and sitting simply without thinking or doing any task.
But shutting off the power is like you are not breathing, your heart is not pumping blood etc etc.
As noted by others, the processor needs to do low priority system tasks during idle time as well as coordinate the proper working of other modules. Looking more deeper will get you into lot of questions.
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#8 Sintharius

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Posted 31 January 2015 - 02:48 AM

If you wish to have a peek into what your system is doing when it's idle, you can use Process Monitor by Sysinternals. It'll give you an insight into what your system is doing at any moment.

As Nikhil_CV said, going deeper will bring up a lot of questions. You can study them if you are interested, but I generally prefer to leave it alone knowing that my system is running well.




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