Messages in this thread | | | Date | Sun, 18 Jan 2009 20:08:49 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: put trigger in to detect mismatched apic versions. |
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* Jack Steiner <steiner@sgi.com> wrote:
> > Btw, I checked with our UV architect and the problem is that we need a > > 16 bit apic id which is what caused the MAX_APICS to be bumped to 32k. > > The lower 8 bits are the normal apic id, and the upper bit relate to > > the node. This means cpu 0 on node 0 has the same apic id as cpu 0 on > > node 1, etc. I also asked about whether we could rely on always > > having > > Not strictly true. The apicids in the ACPI tables are always globally > unique across the entire system. Because of the size of UV systems, UV > needs 16 bit apicids. This fits in the ACPI apicid id/eid fields. > > The actual processor apicid register is unfortunately only 11 bits and > there are some restrictions on the actual values loaded into the apicid > register. > > If we can put unique ids into the apicid register, we do. If we can't, > the function that reads the apicid will automatically supply the rest of > the bits. Most of the kernel is unaware that the processor apicid > register may have only a subset of the bits that are in the ACPI tables.
apicid remapping is something we need/want, so we cannot remove that array. But it would be nice to offload such properties to the percpu area instead - is there any reason why that is hard? The local apic is attached to a CPU in any case. Is there some early init reason that complicates this?
Ingo
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