On 06/13/2007 09:39 AM, Myles Watson wrote:
I'm using LinuxBIOS on my Tyan s2892. I have a device that maps a lot of the memory space, but I'm struggling trying to get the Opteron to read and write to my device in larger blocks. I have set the variable MTRRs in the device driver to writeback (witnessed by /proc/mtrr), but I still get 64-bit accesses instead of 64-byte (cache line).
Some time ago I officially asked an AMD's rep about this. Someone from AMD unofficially said that MemIO can be only Write-Combined. And I gave up with caching.
I'm having the same trouble. Even though the MTRRs are set for write-back, it acts as if it were write-through. I'll keep looking, because it's important to my project.
Thanks for your help and suggestions, Myles