Heinz asks: Are you really Multi-Core?
Submitted by Matt Fleming on Fri, 2006-11-10 10:17.
Heinz writes The Java Specialists' Newsletter. In his latest issue he offers up a little program that will test CPU efficiency...
One of the exercises that we do in the Java 5 course is to measure the CPU cycles that a thread has used, as opposed to elapsed time. If you have one CPU in your machine, then these should be roughly the same. However, when you have several CPUs in your machine, the CPU cycles should be a factor more than the elapsed time. The factor should never be more than the number of actual CPUs, and may be less when you either have other processes running, or too many threads per CPU. Also, as all good computer scientists know, you can never scale completely linearly on one machine, so as you approach a large number of CPUs, the factor will grow more slowly.
The program is attached below; here are the results...
Machine Name: MacBook Pro 15" Machine Model: MacBookPro1,1 Processor Name: Intel Core Duo Processor Speed: 2.16 GHz Number Of Processors: 1 Total Number Of Cores: 2 L2 Cache (per processor): 2 MB Memory: 2 GB Bus Speed: 667 MHz java version "1.5.0_06" Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-112) Java HotSpot(TM) Client VM (build 1.5.0_06-64, mixed mode, sharing) //2 Threads Thread[Thread-1,5,main]: cpuTime = 2030798000 Thread[Thread-0,5,main]: cpuTime = 2057838000 Total elapsed time 2075417000 Total thread CPU time 4088636000 Factor: 1.97 //4 Threads Thread[Thread-2,5,main]: cpuTime = 2047872000 Thread[Thread-1,5,main]: cpuTime = 2053035000 Thread[Thread-3,5,main]: cpuTime = 2048781000 Thread[Thread-0,5,main]: cpuTime = 2061850000 Total elapsed time 4212640000 Total thread CPU time 8211538000 Factor: 1.95 //6 Threads Thread[Thread-2,5,main]: cpuTime = 2030112000 Thread[Thread-3,5,main]: cpuTime = 2045655000 Thread[Thread-5,5,main]: cpuTime = 2041642000 Thread[Thread-4,5,main]: cpuTime = 2034341000 Thread[Thread-1,5,main]: cpuTime = 2036640000 Thread[Thread-0,5,main]: cpuTime = 2060328000 Total elapsed time 6227081000 Total thread CPU time 12248718000 Factor: 1.97