PCIe, power management, and problematic BIOSes
Posted Jul 12, 2011 13:56 UTC (Tue) by farnz
In reply to: PCIe, power management, and problematic BIOSes
Parent article: PCIe, power management, and problematic BIOSes
In Raymond's example, the implementation handles a detected lie by assuming that DoesDriverSupport always returns FALSE, and not using the accelerated paths. In other words, if you're ever caught lying, you're never going to be trusted to do anything sophisticated, even if you could do some acceleration.
Unfortunately, too many people buy hardware on the basis of benchmarks - for an example, look at the QUACK.EXE incident - a GPU driver was set up to detect a specific application used as a benchmark, and cheat.
The problem for buyers of devices with complex drivers is that until you work out what the cheats are, you don't know whether the driver is fast in benchmarks because it cheats, or because it's buggy, or because it's genuinely that fast, or because your applications are buggy and relying on things not guaranteed by the API. Add in closed-source drivers, which can do things like detect the presence of WHQL certification tests on the machine, and you end up with a driver that (for example) is slow and stable when you run the WHQL test suite (thus always passes), but takes shortcuts when WHQL is not running. As benchmarkers rarely have WHQL installed, the driver author gets the "best" of both worlds - stability if you try and test it with WHQL (so you have a WHQL-compliant driver), and fast if you try and benchmark it without WHQL.
Now throw in the idea that applications don't use complex functionality at first, and you see just how painful things can get - the bit that fails on you might be something that no application today uses, at which point it can be years before anyone writes test code that shows the problem is the driver. For some classes of driver (e.g. graphics drivers), people build up a whole set of mythology around things you cannot do, and you develop a set of shared assumptions that aren't actually in the spec, but that "everyone knows" are things that don't work, because drivers traditionally cheated.
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