Messages in this thread | | | Date | Tue, 20 Nov 2007 12:35:22 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: [rfc 08/45] cpu alloc: x86 support |
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On Tue, 20 Nov 2007, Andi Kleen wrote:
> > So I think we have a 2GB area right? > > For everything that needs the -31bit offsets; that is everything linked
Of course.
> > 1GB kernel > > 1GB - 1x per cpu area (128M?) modules? > > cpu aree 0 > > ---- 2GB limit > > cpu area 1 > > cpu area 2 > > .... > > > > For that we would need to move the kernel down a bit. Can we do that? > > The kernel model requires kernel and modules and everything else > linked be in negative -31bit space. That is how the kernel code model is > defined.
Right so I could move the kernel to
#define __PAGE_OFFSET _AC(0xffff810000000000, UL) #define __START_KERNEL_map_AC(0xfffffff800000000, UL) #define KERNEL_TEXT_START _AC(0xfffffff800000000, UL) 30 bits = 1GB for kernel text #define MODULES_VADDR _AC(0xfffffff880000000, UL) 30 bits = 1GB for modules #define MODULES_END _AC(0xfffffff8f0000000, UL) #define CPU_AREA_BASE _AC(0xfffffff8f0000000, UL) 31 bits 256MB for cpu area 0 #define CPU_AREA_BASE1 _AC(0xfffffff900000000, UL) More cpu areas for higher numbered processors #define CPU_AREA_END _AC(0xffffffffffff0000, UL)
> You could in theory move the modules, but then you would need to implement > a full PIC dynamic linker for them first and also increase runtime overhead > for them because they would need to use a GOT/PLT.
Why is it not possible to move the kernel lower while keeping bit 31 1?
> I suspect all of this would cause far more overhead all over the kernel than > you could ever save with the per cpu data in your fast paths.
Moving the kernel down a bit seems to be trivial without any of the weird solutions.
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