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

JVM Tutorials - Herong's Tutorial Examples

∟CPU Impact of Multi-Thread Applications

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

This section provides a tutorial example on how a multi-threaded process behaves on a 2-CPU-4-Thread architecture. A Java process with more than 4 CPU intensive threads gets the same total productivity rate as 4 threads.

Okay, time to play with 3, 4 and more threads.

1. Close all applications on the system.

2. Launch MultithreadingCpuRunner.java with 3 threads.

C:\>"\Program Files\Java\jdk1.7.0_45\bin\java" 
   MultithreadingCpuRunner 1000 3

Thread parameter: 1000
Number of threads: 3
Seconds | Productivity per thread | Total | Average
...
226 | 467 791 513 | 1773 | 1773
227 | 466 754 544 | 1772 | 1773
228 | 467 803 502 | 1775 | 1773
229 | 467 757 548 | 1772 | 1773
230 | 466 815 491 | 1773 | 1773
...

These performance numbers are expected based on the single thread performance and how Windows allocates CPU-Threads. The expectation is that 3 CPU-Threads are allocated with a maximum of (100+100+11)% CPU execution power. That means a maximum of 885*211% = 1867 productivity.

3. Stop and start again MultithreadingCpuRunner.java with 4 threads.

C:\>"\Program Files\Java\jdk1.7.0_45\bin\java" 
   MultithreadingCpuRunner 1000 4

Thread parameter: 1000
Number of threads: 4
Seconds | Productivity per thread | Total | Average
...
165 | 461 454 459 462 | 1838 | 1854
166 | 466 444 464 466 | 1842 | 1854
167 | 466 446 464 467 | 1844 | 1854
168 | 466 463 466 467 | 1863 | 1854
169 | 466 462 465 467 | 1862 | 1854
...

These performance numbers are also expected based on the single thread performance and how Windows allocates CPU-Threads. The expectation is that 4 CPU-Threads are allocated with a maximum of (100+11+100+11)% CPU execution power. That means a maximum of 885*222% = 1965 productivity.

4. Stop and start again MultithreadingCpuRunner.java with 8 threads.

C:\>"\Program Files\Java\jdk1.7.0_45\bin\java" 
   MultithreadingCpuRunner 1000 8

Thread parameter: 1000
Number of threads: 8
Seconds | Productivity per thread | Total | Average
...
136 | 465 167 173 148 142 467 150 140 | 1853 | 1853
137 | 463 143 142 145 142 466 174 176 | 1856 | 1853
138 | 464 136 146 154 172 466 151 156 | 1850 | 1853
139 | 464 161 144 178 158 466 139 140 | 1854 | 1853
140 | 464 163 169 149 145 466 151 143 | 1851 | 1853
...

These performance numbers still match our expectation based on the single thread performance and how Windows allocates CPU-Threads. The expectation is that 4 CPU-Threads are allocated with a (100+11+100+11)% CPU execution power. The total productivity should stay at the same level as running it in 4 threads.

Conclusion: On a 2-CPU-4-Thread machine, HotSpot 1.7 JVM on Windows 7 supports the following default behavior for CPU intensive process threads:

Windows assumes equal CPU power for all 4 CPU-Threads. The processing power of each CPU-Thread is not equal. The total processing power is equivalent to 2.22 (1.00+0.11+1.00+0.11) real CPUs.
Windows allocates only 1/4 CPU-Threads power to a 1-thread Java process, 2/4 CPU-Threads power to a 2-thread Java process, 3/4 CPU-Threads to a 3-thread Java process, and 4/4 CPU-Threads power to a 4-thread Java process.
When running a Java process with more than 4 threads, each thread will be executed slower. But the total productivity of all threads is the same as the 4-thread Java process.

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