"Yesterday, Rik van Riel, William Lee Irwin and myself
were able to discuss this issue of Athlon/AGP instability with AMD.
This converation was very enlightening, to say the least.
Let's start with some facts. The issue that is being discussed
here is not related to the so-called "INVPLG bug". So, what is the
issue, and who's at fault? Yesterday, AMD offered us an explanation
of what may be happening to cause AGP instability on Linux systems.
This explanation appears to be the exact scenario that bit Windows
2000 in September 2000. AMD characterizes this issue as a cache
coherency problem resulting from how other components on the
motherboard (the GART in particular) interact with a particular
performance-enhancing feature of the Athlon Processor called
speculative writes. The GART and the CPU have two different views
of memory -- the GART's view does not "see" the contents of the
Athlon's internal caches, and herein lies the problem. In certain
situations the CPU and the GART can step on each other's toes,
resulting in memory corruption. For more information, see my Linux
kernel mailing list post that contains an explanation of this
particular problem in AMD's own words."
