Single Thread Process on 2-CPU-4-Thread Machine

JVM Tutorials - Herong's Tutorial Examples

∟CPU Impact of Multi-Thread Applications

∟Single Thread Process on 2-CPU-4-Thread Machine

This section provides a tutorial example on how a single-threaded process behaves on a 2-CPU-4-Thread architecture. Windows will only allocate a total of 1 CPU-Thread to the process.

To get further understanding of the performance impact of the CPU architecture, let's try the following tests my Intel Core i5-2520M, which is a 2-CPU-4-Thread architecture.

First, let's play with a single-thread process only.

1. Close all applications on the system.

2. Launch MultithreadingCpuRunner.java with 1 thread.

C:\>"\Program Files\Java\jdk1.7.0_45\bin\java" 
   MultithreadingCpuRunner 1000 1

Thread parameter: 1000
Number of threads: 1
Seconds | Productivity per thread | Total | Average
...
181 | 883 | 883 | 885
182 | 890 | 890 | 885
183 | 886 | 886 | 885
184 | 882 | 882 | 885
185 | 888 | 888 | 885
...

3. View individual CPU-Thread usage on the Performance tab of Task Manager. You will see that the running process is being distributed between 2 CPU-Threads with 2 other CPU-Threads doing nothing:

CPU-Thread 1 - 85% used (approximately)
CPU-Thread 2 -  0% used
CPU-Thread 3 - 15% used (approximately)
CPU-Thread 4 -  0% used

4. View total CPU usage on the Performance tab of Task Manager. You will that the total CPU usage is about 24%. See the picture below:
1 Thread Running on 4 CPU-Threads

Question: Why the JVM is not make full use of all 4 CPU-Threads? I have no idea.

5. Force Windows to use only 1 CPU-Thread by going to the on the Processes tab of Task Manager. Then right-mouse click on the "java.exe" process, which represents the running MultithreadingCpuRunner.java program. When select "Set Affinity...", you will see the processor affinity options. Uncheck CPU 1, 2, and 3. Then click OK to force Windows to only use CPU-Thread 0 for the execution of MultithreadingCpuRunner.java. See the picture below:
Set Affinity - Using 1 CPU Only

6. Go back to view individual CPU-Thread usage on the Performance tab of Task Manager again. You will see that the running process is being distributed only to the first CPU-Thread:

CPU-Thread 1 - 100% used
CPU-Thread 2 -   0% used
CPU-Thread 3 -   0% used
CPU-Thread 4 -   0% used

This behavior is expected, because we asked the Windows to only use the first CPU-Thread. Of course, the overall performance is not changed:

Seconds | Productivity per thread | Total | Average
...
1163 | 885 | 885 | 885
1164 | 892 | 892 | 885
1165 | 889 | 889 | 885
1166 | 880 | 880 | 885
1167 | 891 | 891 | 885
...

Conclusion: By default, Windows distributes a single process to more than one CPU-Threads to execute. But the it will only allocate a total of a single CPU-Thread power to the process. For example, Windows will allocate 25% of total CPU power to a single-threaded process on a 4-CPU-Thread machine.

Last update: 2014.

Table of Contents

About This Book

Downloading and Installing JDK 1.8.0 on Windows

Downloading and Installing JDK 1.7.0 on Windows

java.lang.Runtime Class - The JVM Instance

java.lang.System Class - The Operating System

ClassLoader Class - Class Loaders

Class Class - Class Reflections

Sun's JVM - Java HotSpot VM

JRockit JVM 28.2.7 by Oracle Corporation

JVM Runtime Data Areas