Messages in this thread | | | Date | Tue, 20 Nov 2007 18:08:38 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: [rfc 08/45] cpu alloc: x86 support |
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On Wed, 21 Nov 2007, Andi Kleen wrote:
> On Wednesday 21 November 2007 02:16:11 Christoph Lameter wrote: > > But one can subtract too... > > The linker cannot subtract (unless you add a new relocation types)
The compiler knows and emits assembly to compensate.
> All you need is a 2MB area (16MB is too large if you really > want 16k CPUs someday) somewhere in the -2GB or probably better > in +2GB. Then the linker puts stuff in there and you use > the offsets for referencing relative to %gs.
2MB * 16k = 32GB. Even with 4k cpus we will have 2M * 4k = 8GB both do not fit in the 2GB area.
The offset relative to %gs cannot be used if you have a loop and are calculating the addresses for all instances. That is what we are talking about. The CPU_xxx operations that are using the %gs register are fine and are not affected by the changes we are discussing.
> Then for all CPUs (including CPU #0) you put the real mapping > somewhere else, copy the reference data there (which also doesn't need > to be on the offset the linker assigned, just on a constant offset > from it somewhere in the normal kernel data) and off you go.
Real mapping? We have constant offsets after this patchset. I do not get what you are planning here.
> Then the reference data would be initdata and eventually freed. > That is similar to how the current per cpu data works.
Yes that is also how the current patchset works. I just do not understand what you want changed.
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