In particular, AMD Radeon GPU hangs have been quite common on the release candidates thus far of Linux 3.15. For the past few weeks I have been running into hangs when running demanding OpenGL processes on a system with various Radeon HD 7000 / Rx 200 series graphics cards. Fortunately, a few days ago there's been some upstream notice and work around the issue.
Marek Olšák on Friday reported CIK hangs with kernel 3.15. The AMD open-source developer bisected it and found an issue going back to 3.15-rc1. There were also reports of other users experiencing similar Radeon hardware problems on Linux 3.15. Christian König, the AMD developer responsible for the faulty commit, posted a patch to attempt to fix the issue on Monday. [PATCH] drm/radeon: fix page directory update size estimation. While this patch hasn't yet been mainlined within the Linux 3.15 kernel, it appears to take care of the fallout for those that have tried the small patch, but there's still apparently a performance regression at hand.
Over the past few days I've been working on a big Intel vs. Nouveau vs. Radeon open-source graphics card comparison, albeit that article coming out in the next day or two is limited on the AMD side due to fallout from these issues. Xonotic is one of the games to easily reproduce the 3.15 problems, which of course, is a very common test to the Phoronix Test Suite. When the Radeon issues are settled in upstream Linux 3.15, I'll run some other sort of driver benchmarks. It's also overdue for some new Windows vs. Linux driver benchmarks and open-source vs. closed-source GPU driver tests.
Fortunately, for those that recall, the new PTS / OpenBenchmarking.org test farm is still coming. It was delayed most recently by limited electrical capacity and leaky ceilings/walls, but at the end of June will be moving to a new home/office to allow for plenty more space and electrical capacity. With the daily and per-commit testing of important components like Mesa and the Linux kernel, these issues will be caught on our side much more quickly and with our automated testing software be more helpful in reporting the information to the appropriate sources.