CrossFireX Arrives: First Look at 3 and 4 GPUs in 2 Card Setups
by Derek Wilson on March 7, 2008 12:05 PM EST- Posted in
- GPUs
… and Tearing it Down
Whether the problems we saw end up being very isolated problems or not, it's always good to be cautious. Now, let's move on to the part that will absolutely affect everyone who runs CrossFireX at some point: uninstalling the hardware. Until now, if we needed to step down to one card all we needed to do was remove the hardware and everything would be fine. AMD tells us that because CrossFireX uses Windows Vista's Linked Display Adapter (LDA) technique for combining multiple physical graphics cards into one virtual device, this is no longer as simple.
Before removing a card from the system, you MUST disable CrossFireX or uninstall the driver. If you do not disable CrossFireX, the driver will fail to load the next time the system boots. There will be no way (from what we can tell) to disable CrossFireX if the driver doesn't load. Thus, the driver will need to be uninstalled anyway. If you want to keep one card in the system, be sure to disable CrossFireX first or you will have to uninstall and reinstall your driver.
We've asked for more details about why this isn't something AMD can handle in the driver, and this is what we understand so far. After LDA mode is set up, a specific number of physical devices are expected when the driver tries to load. If there is only one card present, this looks the same as if the link failed and thus the driver won't load. AMD has said that this is the expected behavior based on how Vista handles LDA. Our position is that if this is the case, it is a design flaw in Vista that Microsoft needs to address.
After speaking with AMD on this, they have said they would try to make the documentation about how to handle uninstalling hardware properly as prominent as possible. While it's not ideal, thorough documentation of the issues is definitely a good thing to have when potential issues are very likely to arise.
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kilkennycat - Saturday, March 8, 2008 - link
Multi-chip hybrid substrates with widely-spaced dies can help to spread out the heat rather nicely and help keep the overall yield up too, as Intel has demonstrated with the quad Core 2 processors. I fully expect hybrid substrates to become a popular interim solution to the need for masively-parallel processing GPUs -like IBMs 20-chip solution for their big number-crunchers. The hybrid/chip combo- architecture can be designed to externally emulate a single GPU. Also a very nice way of adding some extra local memory if necessary.DerekWilson - Saturday, March 8, 2008 - link
i agree that this is good direction to go, but even with intel we've still got dual socket boards for multicore chips ...the real answer for the end user is always get as fast a single card as possible and if you need more than one make it as few and as powerful cards as you can.
e6600 - Saturday, March 8, 2008 - link
no crysis benchies?Slash3 - Saturday, March 8, 2008 - link
Crysis is broken as a benchmark... despite all pre-release hype, the game seems to scale very badly across multiple cores and multiple GPUs. It's is kind of unfortunate, as if there's one game that could benefit from efficient scaling, it's Crysis.JarredWalton - Saturday, March 8, 2008 - link
I'm curious to see if version 1.2 fixes anything... it might. That just came out yesterday, so I don't think many have had a chance to look at whether or not performance changed.[Just checked]
At least for single GPUs, I see no real change in performance. I haven't had a chance to test multi-GPU, and all I have right now is SLI and CrossFire. Could be that v1.2 will help more with 3-way and 4-way configs. We'll see.
DerekWilson - Saturday, March 8, 2008 - link
there was no perf benefit at all from going to 3 or 4 gpus ... we saw this in our preview and when we tested the 8.3 driver. we mention that on the test page ...