30.08.2012, 16:04, "Thiago Macieira" <thiago.macie...@intel.com>: > 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 > operations. > > 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. >
I guess that all of these facts apply to building on Linux. As for Mac, I have a feeling that OS scheduler is somewhat more fair there, and complete CPU utilization is achieved with lesser threads. -- Regards, Konstantin _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
