Kenneth Culver wrote: > > There's actually a seperate TLB bug, but FreeBSD doesn't > > trigger that one, either (Linux can tickle it, when there > > are certain specific circumstances met). > > Well, I think I know what you're talking about, linux allocates agpgart > memory without setting a "non-cacheable" bit, and then the agp card writes > to that memory, but the cpu cached it already, which makes the cache wrong > or something like that, and causes the crashes/hangs. I know this is a > greatly simplified version of the real problem, but I think this is a > linux bug not necesarily an amd bug.
No, you are describing the coherency bug in the chipset used for the AGP with AMD processors, which should enforce a coherency cycle, and cache invalidation for AGP based writes of the shared memory region. They are treating it as if it were non-cacheable dual ported SDRAM. There *really* is a bug in P4 and above and in late model AMD chips with 4M pages. It is very easy to reproduce with a few small kernel modifications (to actively use 4M pages) and 256M-512M of RAM. I'll characterize it further and provide the software workaround, for $10,000. It's about 16 machine instructions, if you write it out as code. Meanwhile, Linux and Windows can keep turning off the PSE, and losing 4-14% of their performance, depending on their application. -- Terry To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-current" in the body of the message
