Messages in this thread |  | | | From | Charles Buysschaert <> | | Subject | RE: Speed of RAM reserved with memmap kernel command line option. | | Date | Fri, 28 Oct 2011 09:30:22 +0000 |
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Hello Matthias,
Thanks for your feedback.
>Smells to me like you are missing a mapping in MTRR ... >Documentation/x86/mtrr.txt
I checked and those definitely look correct:
This is the physical ram map at boot:
[ 0.000000] user-defined physical RAM map: [ 0.000000] user: 0000000000000000 - 0000000000096800 (usable) [ 0.000000] user: 0000000000096800 - 00000000000a0000 (reserved) [ 0.000000] user: 00000000000e4c00 - 0000000000100000 (reserved) [ 0.000000] user: 0000000000100000 - 0000000040000000 (usable) [ 0.000000] user: 0000000040000000 - 0000000060000000 (reserved) [ 0.000000] user: 0000000060000000 - 00000000bf780000 (usable) [ 0.000000] user: 00000000bf780000 - 00000000bf798000 (ACPI data) [ 0.000000] user: 00000000bf798000 - 00000000bf7dc000 (ACPI NVS) [ 0.000000] user: 00000000bf7dc000 - 00000000c0000000 (reserved) [ 0.000000] user: 00000000fee00000 - 00000000fee01000 (reserved) [ 0.000000] user: 00000000ffe00000 - 0000000100000000 (reserved) [ 0.000000] user: 0000000100000000 - 00000001c0000000 (usable) And this is the MTRR contents.
$ cat /proc/mtrr reg00: base=0x1c0000000 ( 7168MB), size= 1024MB, count=1: uncachable reg01: base=0x000000000 ( 0MB), size= 8192MB, count=1: write-back reg02: base=0x0c0000000 ( 3072MB), size= 1024MB, count=1: uncachable reg03: base=0x0bf800000 ( 3064MB), size= 8MB, count=1: uncachable The reserved zone is indeed marked as 'reserved' 512Mb located at 1Go. And this zone is covered by the reg01 MTRR without being overriden by anyother, so it's 'write-back' which is good.
> ... or PAT. > Documentation/x86/pat.txt This is also what we tried to set by modifying the protection field given to the remap_pfn_range.
we dumped the kernel_page_tables file provided by "debugfs", and we can see the following entry: 0xFFFF880040000000 -> 0xFFFF880060000000 512M RW PCD PSE GLB NX pmd I am not 100% sure it is the mapping of my "0000000040000000" physical address, but it looks like (is there a way to see which physical address it relates to?). I can see the flag "PCD" Page Cache Disabled. Does the kernel automatically create a mapping for memory reserved with "memmap=" option? Would "aliasing" be the reason why my "remap_pfn_range" seems to ignore the vma->vm_page_prot we are setting? ( static inline pgprot_t pgprot_cached(pgprot_t _prot) { unsigned long prot = pgprot_val(_prot); prot = (prot & ~_CACHE_MASK); return __pgprot(prot); } vma->vm_page_prot = pgprot_cached(vma->vm_page_prot); remap_pfn_range(vma, vma->vm_start, myboard_var[board].dmablkp>>PAGE_SHIFT,DMA_BUFFER_SIZE, vma->vm_page_prot) ) Thanks for your help,
Charles
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