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Mixed Vendor / Cards Setup

We first started to test Crossfire with mixed vendor / cards setup, using cards from three different vendors - Gigabyte, MSI and Sapphire. Since the Gigabyte was the odd one out (it didn't use the same board design as the other two), we opt to start with the Sapphire Radeon X1950 Pro and MSI RX1950 Pro. First, we put the Sapphire card in the first PCI-E x16 slot and the MSI card on the second and then install the two Crossfire bridges. After Windows detected the second card and install the appropriate driver, we restarted the PC. Then we enable Crossfire and started testing,  however we we immediately noticed display corruption everytime we entered full screen 3D mode. We tried switching Catalyst AI mode and even swapping the card but that didn't fix the problem.

So, we decided to use the Gigabyte Radeon X1950 Pro instead of the Sapphire card. After some initial testing, we found the only workable Crossfire setup is to put the Gigabyte card in the first slot and the MSI card in the second slot. Using the MSI card on the first slot will trigger a BSOD everytime we enter Windows. It's pretty likely this issue is driver related, the BSOD basically occured when Windows detects the new card. With the above setup, everything seems to be in order.

At least, that's what we thought. During testing, we encounter some very odd behaviour with our Crossfire setup, mainly with Quake 4 and The Elder Scrolls IV: Oblivion. We saw a huge performance drop in Quake 4 at 1280 x 1024 and 1600 x 1200, both with AA and AF and without. On some parts of the benchmark, the frame rate will slow to a crawling 30 fps at precisely the same point. In Oblivion, the Crossfire setup seems to be leaking (graphics) memory like crazy after about half an hour of gameplay.

	1024x768	1280x1024	1600x1200
Min	141	32	31
Avg	206.206	134.419	110.845
Maxi	248	331	215

We e-mailed an ATI representative about these problems and he asked us what cards are we using so that they can reproduce the problem. We sent a full description of the problem and information about the setup and tests we used. Unfortunately, we haven't heard any response about these issues to this day. However, searching the web, we found one possible explanation for the display corruption we saw with the Sapphire card in TechPowerUp's forums (here). The problem seem to be caused by different BIOS used by the cards - using the same BIOS supposedly fix the problem - we didn't try flashing the BIOS for two reasons. One, ATI did promise there won't be any problem with using mixed vendor / cards and two. flashing the BIOS does involve some risks, more so if you're using cards from different vendors.

After some time tinkering, we found the problem with Quake 4 (and Oblivion) is that the Crossfire setup (or more precisely, the Catalyst drivers) seem to have a bug of 'flushing' or clearing the graphics memory. In Quake 4, the trigger is applying system changes or in our case executing the command 'vid_restart'. The workaround to this problem is simple - after applying system changes, quit the game to the desktop and then restart the game.

	With 'vid_restart'			With application restart
	1024x768	1280x1024	1600x1200	1024x768	1280x1024	1600x1200
Min	141	32	31	138	108	82
Avg	206.206	134.419	110.845	213.927	170.964	136.903
Maxi	248	331	215	311	255	204

A very huge difference in minimum fps and significant difference in average fps. So, we tried using the same workaround in Oblivion and - it works! Just like Quake 4, the trigger was entering / exiting maps, like you do when you enter / exit a town or a building (or fast travelling). Frame rates will drop to the teens, but after a save (on the same spot) and a restart, frame rates went up to where it's supposed to be (30 to 50 fps depending on the scene).

Before using this workaround, we also tried using identical cards (two Gigabyte Radeon X1950 Pro), but the problem still persists.  Clearly, the performance drops we're seeing are driver related. Using the latest Catalyst 7.3 didn't help, so hopefully this will be addressed in the next driver release. We certainly hope ATI will also address the issues with Crossfire installation with mixed vendor / cards. At the moment, we don't think you should use mixed vendor / cards setup , so if you want to use Crossfire, you better use two identical cards from the start. The question is - is it worth the hassle? We'll examine the performance Crossfire has to offer next.

Performance

Graphical settings for these games are set to their highest possible values. Notable differences are F.E.A.R where we disable "Soft Shadows", Quake 4 where we use High Quality - not Ultra Quality - but anisotropic filtering was set to "1" for default tests and "16" for AA / AF tests. We used Serious Sam II built in "Maximum" quality preset then change resolution and AA / AF settings accordingly. All of these settings can be seen here. Our TES IV: Oblivion settings are as close as we can get to Ultra High Quality - you can see our test settings here. For Need for Speed: Carbon, we used the game's "Maximum" video quality preset, but change the filtering to "Trilinear" for default tests - AA AF tests are run with "4x" and "Anistropic". NFS: Carbon test were done with the Sprint Race on Lincoln Boulevard. You can see the settings we used for GTR 2 here. Clear weather was used for our run of Monza GP tests.

Our test setup
Intel Core 2 Duo E6300 socket LGA-775 (running at 7 x 400 MHz)
4 x 512 MB A-DATA Vitesta 5-5-5-18 PC6400 DDR2-SDRAM
Gigabyte Radeon X1950 Pro 256 MB graphics card
Gigabyte P965-DS3P Intel P965 motherboard
Maxtor DiamondMaxPlus9 80 GBs Serial ATA 8 MB buffer
LiteOn 1673S DVD-RW
Tagan TG530-U15 530 watts ATX/BTX power supply

Windows XP Professional with Service Pack 2 installed
ATI Catalyst 7.2 and 7.3 reference driver
Intel Chipset Software Installation Utility 8.1.0.1006
DirectX 9.0c
all respected games used for benchmarks have been updated to their latest, final builds.

We'd like to thank Gigabyte for providing the Gigabyte P965-DS3P motherboard and the Gigabyte Radeon X1950 Pro graphics card for this test. We'd also like to thank Tagan for the Tagan TG530-U15 power supply.

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