TLDR; My machine freezes when using CrossfireX and I'm looking for a way to fix it. Behaviour description first, specs at the end.
I recently upgraded my computer and I thought I would try CrossfireX in games. Unfortunately, it causes system freezes. It is not a big deal as the main reason for the upgrade was OpenCL (mining) and the games run very well with a single card, but why not use them both? The character of the freeze is a hard system lockup. There is no BSOD or display corruption, the freeze-time picture is stuck. There is nothing in the log files, or in other words, the end of the log file is corrupt because the file system wrote the file size change before updating the content.
The freeze happens both with Windows 7 Ultimate 64 and Ubuntu 14.04 64, but it manifests itself slightly differently. On Windows, it freezes within about second after the game turns on CrossfireX (which I can see after enabling the show logo option in Catalyst Control Center), for example after turning on the fullscreen mode on. The mouse cursor can briefly move after the CrossfireX logo shows up but almost immediately freezes as described above. Without running a crossfire-enabled game, it works fine. On Linux, after turning CrossfireX on, X does not start anymore, I have to boot into rescue mode and manually remove the crossfire definition chains from the config file (amdconfig does not want to make the modification without X, and X freezes, so I have to edit the file directly, the file name is something like /etc/amd/amdpcsdb). Windows and Linux are each on a different drive (Win on HDD & Lin on SSD).
The apps that I tried are World of Warcraft, Planetside 2 and the Passmark PerformanceTest 8.0. GPU-Z displays that Crossfire is on but does not cause a freeze (I suppose it does not try to actually use it).
I tried the latest stable and beta Catalyst drivers without any changes. I flashed the BIOS to the latest available version and again no change. Windows was freshly installed when I upgraded the hardware a couple of weeks ago.
I don't think it has to do with power or cooling, as with OpenCL I can fully load both GPUs for hours without any problems, and the temps stay below 80 (below 70 on the bottom card). I'm trying to mod the case to add fans so that the temps are even lower. I also tried to do proper cable management (most cables are below the mainboard) to improve airflow and so that they don't get stuck in the fans or something, and I also removed some inside case parts to further improve the flow.
Without CrossfireX, there are no problems with the machine whatsoever. I do overclock my CPU slightly (5%) but turning it off does not change anything. I can't think of any obvious reason why the freeze occurs, only some weird incompatibility (like having different models of monitors).
Antec P183 Case, 2 intake fans in the front, 2 exhaust fans (top+rear)
AMD Phenom II X4 965BE, Noctua NH-U12P Cooler, 1 push fan (the rear exhaust fan is right behind the other side of the fan)
Asrock 970 Extreme 3 R2.0 Mainboard
2 x Sapphire D5 R9 290 Tri-X
Xilence Modular 1000W PSU
Hitachi 1TB HDD, Intel 160GB SSD
2 LG monitors (L226WTQ-SF and W2252TQ-PF), both connected to the primary card
Let me know what you think and if you need more info.