Wink Saville’s Blog

I wanted to time how fast different approaches might be in for dispatching to states in a state machine. At first I used android.os.SystemClock.uptimeMillis() but I thought there should be something more portable. I did a web search and found that in Java 5.0 System.nanoTime() was added and in fact found that it is implemented in Android so I abstracted away the time base:

static final long readTsc() {
    return System.nanoTime();
}

static final double tscToSecs(long tsc) {
    return tsc / 1000000000.0;
}

I also tested the speed of 10 in a row and when executing on the android emulator I get the following:

V/TestSm ( 586): s[0]=1376737118000 diff=0.000000ns
V/TestSm ( 586): s[1]=1376737159000 diff=41000.000000ns
V/TestSm ( 586): s[2]=1376737178000 diff=19000.000000ns
V/TestSm ( 586): s[3]=1376737196000 diff=18000.000000ns
V/TestSm ( 586): s[4]=1376737214000 diff=18000.000000ns
V/TestSm ( 586): s[5]=1376737231000 diff=17000.000000ns V/TestSm ( 586): s[6]=1376737249000 diff=18000.000000ns
V/TestSm ( 586): s[7]=1376737267000 diff=18000.000000ns
V/TestSm ( 586): s[8]=1376737285000 diff=18000.000000ns
V/TestSm ( 586): s[9]=1376737302000 diff=17000.000000ns

When I execute this on my Intel developement system, a 6600 @ 2.4GHz the following is seen:

Tests: s[0]=15759382032271 diff=0ns
Tests: s[1]=15759382033117 diff=846ns
Tests: s[2]=15759382033529 diff=412ns
Tests: s[3]=15759382033918 diff=389ns
Tests: s[4]=15759382034300 diff=382ns
Tests: s[5]=15759382034693 diff=393ns
Tests: s[6]=15759382035083 diff=390ns
Tests: s[7]=15759382035442 diff=359ns
Tests: s[8]=15759382035801 diff=359ns
Tests: s[9]=15759382036161 diff=360ns

Greater than 40 times faster on my Intel box than the android editor. That would be expected, but even 41us isn’t too bad compared to the 439us for the android.os.SystemClock.uptimeMillis().

I’ve also created a class so I can easily use this as I develop the state machine code:

package com.saville.debug.android;

public final class Timing {
	public static final long readTsc() {
		return System.nanoTime();
	}

	public static final double tscToSecs(long tsc) {
		return (tsc / 1000000000.0);
	}

	public static final double tscToMillis(long tsc) {
		return (tsc / 1000000.0);
	}

	public static final double tscToUsecs(long tsc) {
		return (tsc / 1000.0);
	}

	public static final double tscToNanos(long tsc) {
		return ((double)tsc);
	}
}