> Myles Watson wrote: > >> On 6/13/07, Myles Watson <[EMAIL PROTECTED]> 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). > >>> > >> wirte-back or write-combining? > >> > >> YH
> > I did write-back, because I would like it to be treated as much like > > DRAM as possible. > > > > Myles > > > Hi Myles, > I am not an Opteron expert but here are a few items you might want to > check. > > I assume that this is a PCI/E/X device. Is the device memory BAR and > bridge memory set as prefetchable? It is HyperTransport, but pretty much the same. I set it as prefetchable. The reads actually work, it's the writes that come through 8-bytes at a time. > Check that you don't have any overlapping mtrrs. I think that they > resolve to the most restrictive setting > Check the PAT setting for that memory. The memory page will resolve to > the most restrictive setting. (Note I am not sure if Linux uses PAT) > See section 7.6 of the System Programmers Guide Volume 2. You can get > here: > http://www.amd.com/gb-uk/Processors/TechnicalResources/0,,30_182_739_7044,00 .html I'll look. > You might get some performance by caching the device memory space but I > don't think that it is the best use of the cache. If you are moving a > lot memory between your device and system memory it is best that the > driver DMA it in instead of reading it in with the CPU. I'm using the device to explore paging activity, so I'm not after speed as much as I am trying to make the device seem as much like RAM as possible Thanks for your help, Myles -- linuxbios mailing list [email protected] http://www.linuxbios.org/mailman/listinfo/linuxbios
