[Interest] Slow compiling on Mac

Thiago Macieira thiago.macieira at intel.com
Thu Aug 30 14:04:19 CEST 2012

On quinta-feira, 30 de agosto de 2012 15.52.49, Konstantin Tokarev wrote:
> 1. Compilation is not entirely CPU-bound process.
> 2. OS scheduler is not perfect.

The best performance ratio I can get on my dual core x dual thread machine is 
375% CPU utilisation, so a -j4 would be recommended.

However, I always build with -j5. My benchmarks show that from -j4 to -j6, 
there's minimal difference. if I add more, it starts to slow down again; if I 
use fewer, it idles.

The rationale for using more than your number of CPUs is that there's a lot of 
I/O involved. Reading from disk is unbearably slow compared to other 

I have an SSD, which means it's not that slow, so I don't gain much going from 
-j4 to -j5. But on a mechanical hard drive, that is more pronounced.

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
     Intel Sweden AB - Registration Number: 556189-6027
     Knarrarnäsgatan 15, 164 40 Kista, Stockholm, Sweden
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