Messages in this thread | | | Date | Sun, 26 Oct 2008 17:12:10 -0700 | From | Arjan van de Ven <> | Subject | Re: PAT and MTRRs |
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On Sun, 26 Oct 2008 22:46:21 -0100 "Diego M. Vadell" <dvadell@linuxclusters.com.ar> wrote:
> Hello, > > I have 6 identical PCs (HPC cluster) with MTRR problems. In older > kernels, I had to use "mem=3300M", or else, I would get a very slowly > boot (as when you run out of MTRRs). > > So I thought that PAT would make this lack of MTRRs problem go > away, and upgraded to 2.6.26.6 and 2.6.27.2, but it didn't: I still > get (from dmesg) > > x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106 > WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing 704MB > of RAM. > > Most probably, I understood wrong. I read lwn.net's article [1] > about PAT several times, Documentation/x86/pat.txt , tried to use > mtrr_chunk_size= and mtrr_gran_size= in various combinations (as > discussed in this LKML thread [2]), but I still don't get it. > > So, what did I miss? Am I wrong thinking that PAT is a better MTRR > (wrt setting the cache type of the RAM)? >
PAT can't make memory cachable that the MTRR's have as uncachable. What PAT *can* do is, within an MTRR, do fine grained mapping...
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
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