Daniel Pitts’ Tech Blog

Recently I’ve seen a few attacks on Java’s performance on comp.lang.java.programmer. So, I’ve decided to write my own benchmarks and test it myself. I expected the C version to perform slightly better, but at least in the same range, as the Java version. I was surprised that the Java version performed better, on both the client vm and the server vm.

I did my own benchmarks using these files:

bench.c

#include <stdio.h>
#include <time.h>

void bench() {
  long foo = 0;
  clock_t start = clock();
  for (long i = 1; i < 5000; ++i) {
    for (long j = 1; j < i; ++j) {
      if ((i % j) == 0) {
        foo ++;
      }
    }
  }
  clock_t end = clock();
  printf("%d %dms\n", foo,
     (int) ((end - start) * 1000 / CLOCKS_PER_SEC));
}

int main() {
  for (long i = 1; i < 10; ++i) {
    printf("%d: ", i);
    bench();
  }
}

Bench.java

public class Bench {
  static final long CLOCKS_PER_SEC = 1000;
  static void bench() {
    int foo = 0;
    long start = System.currentTimeMillis();
    for (int i = 1; i < 5000; ++i) {
      for (int j = 1; j < i; ++j) {
        if ((i % j) == 0) {
          foo ++;
        }
      }
    }
    long end = System.currentTimeMillis();
    System.out.printf("%d %dms\n", foo,
       (int) ((end - start) * 1000 / CLOCKS_PER_SEC));
  }

  public static void main(String[] args) {
    for (int i = 1; i < 10; ++i) {
      System.out.printf("%d: ", i);
      bench();
    }
  }
}

Then I ran these:

-bash-3.00$ java -version
java version "1.5.0_09"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_09-b03)
Java HotSpot(TM) Client VM (build 1.5.0_09-b03, mixed mode, sharing)
-bash-3.00$ javac Bench.java
-bash-3.00$ g++ --version
g++ (GCC) 3.3.3 (NetBSD nb3 20040520)
Copyright (C) 2003 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-bash-3.00$ g++ bench.c -o bench

Now I’m ready to run the individual tests:

-bash-3.00$ java -server Bench
1: 38357 457ms
2: 38357 416ms
3: 38357 401ms
4: 38357 394ms
5: 38357 394ms
6: 38357 401ms
7: 38357 395ms
8: 38357 401ms
9: 38357 394ms

-bash-3.00$ java -client Bench
1: 38357 421ms
2: 38357 400ms
3: 38357 394ms
4: 38357 400ms
5: 38357 393ms
6: 38357 393ms
7: 38357 400ms
8: 38357 394ms
9: 38357 401ms

-bash-3.00$ ./bench
1: 38357 450ms
2: 38357 440ms
3: 38357 450ms
4: 38357 430ms
5: 38357 450ms
6: 38357 440ms
7: 38357 450ms
8: 38357 440ms
9: 38357 450ms

As you can see, the Java version is approximately 10% faster than the c version. So, here is my challenge. Why is C so slow? I thought it was supposed to be faster than Java.