Re: How to limit CPU usage within C++ (Linux)

Joe Greer <>
Tue, 19 Aug 2008 12:06:19 +0000 (UTC)
Alexander Dong Back Kim <> wrote in news:8d2a9a1e-78d1-

Dear members,

First of all, I apologize that this question is not 100% pure C++
question so some might be annoyed by this.

I'm writing a multithreading based application. The application can
use flexible number of threads while it's running (between 2~32
threads when it's needed or configured). My development machine has 8
CPU so the application I'm writing sometimes uses 600% of CPU usage
which was very impressive at the beginning. However, since the real
target machine has only 1 CPU and requires to run many other
applications at the same time, I think I should somehow limit the CPU
usage of my application (let say 30%.

I tried to use sleep() but I found out it's not good enough because I
want to explicitly define maximum CPU usage rate for this application.
Any suggestion or recommendation are welcomed and appreciated.


In order to not use CPU time all of your threads have to be occupied doing
something else. That something else can include waiting on a mutex,
sleeping, waiting on the disk, or something else. You can certainly use
some adaptive technique like querying your current cpu usage and adjusting
a sleep based upon whether you have hit your target or not.

However, having said that, I have to discourage you from taking this
approach. A cpu which isn't running at 100% is actually just throwing the
remaining cycles away. That is, there is no concept of saving the CPU for
some other task. The OS will schedule and balance any tasks it has to try
to keep the cpu busy. It even has one that it runs when there aren't any
others. I think what you really want is lower the priority of your whole
process so that if there is any other work to be done, it will be done
first, but at the same time, you will get to use any spare cycles. Of
course, most OS's won't let a process totally starve, so you will get some
time anyway. Usually a program can lower its own priority, but if not,
*nix has the nice command and Windows Task Manager will let you lower your

Hope that helps,

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