Speeding up builds

Here's a really simple tip if you are using GNU make. You can pass in the -j option to run the build steps in parallel. The default is -j1, i.e. no parallising.

The next question is what's the optimum number of jobs to run in parallel? An experiment on a build reveals:

N	Time
1	6m13s
2	3m28s
3	2m38s
4	2m11s
5	1m59s
6	1m55s
7	1m53s
8	1m49s
12	1m47s
16	1m47s

So there you have it! On a 4-core CPU (Intel Q6600), it's best with -j4 or above. It's interesting that -j4 didn't max out the CPUs, and that you can keep getting good improvements up to at least -j8.