Optimus/Primus Regresses On Latest Mesa 10.5.5 Release

A Phoronix reader has pointed out that a regression has slipped into the Mesa 10.5.5 point release that negatively affects users of dual-GPU laptop owners with NVIDIA Optimus technology that are using the open-source "Primus" code for running OpenGL games on the alternate graphics processor.

From this Primus bug report from one week ago, the performance of the dedicated GPU is now lower than that of the Intel HD Graphics... Much lower. When tracking it down, the issue originates with Mesa 10.5.5.

The issue appears related to this Mesa bug report opened yesterday. The Mesa issue is that the PBO glDrawPixels is no longer using the blit fast path. This issue is affecting Mesa 10.5.5 and the Mesa 10.6 series.

There is a patch in the Primus thread to workaround the issue, but as of writing this article there's been no patch to land in mainline Mesa. This is just a warning for anyone out there who depends upon Primus before upgrading to Mesa 10.5.5+ in the next few days.