Compared it with qmake builds with pch: "qm+pch" and without "qm-pch": > -j8 -j1 > merged: 1 1.9 > pch : 1.9 6.4 > plain : 2.2 8.1 > qm+pch: 2.0 5.1 > qm-pch: 2.1 7.6 The error is about 10%. The slowdown for cmake builds with j1 is real, maybe cmakes dependency checker. And I have the impression HT does not help much, similar numbers for -j4.