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Re: [Xen-devel] APIC handling on x86-64

On 19 Mar 2006, at 19:15, Jan Beulich wrote:

Actually, looking further, the originally mentioned adjustment can't work. x86-64 Linux can do this because they deliver IPIs (on large systems) in physical destination mode, and hence they don't really need to values written to DFR and specifically LDR. Since Xen inherited the 32-bit code, IPIs get sent in logical (cluster) mode, and then playing games like this with the LDR is only going to cause problems (you'll hit multiple processors with a send that's intended for a single one only). Hence I would think that more extensive changes are going to be needed; entirely taking x86-64's model may not be feasible either (aside of the fact that this would mean quite extensive code changes), as they don't need
to care about pre-Pentium4 processors.

Yes, that's what stopped me taking x86/64 Linux code originally. I wonder if we can take just the IPI code from x86/64, plus whatever small changes we need to fix problems like this x460 bug. IPI code is reasonably self contained relative to the bulk of the apic code in apic.c. The x86/64 IPI code was a bunch cleaner than the i386 code last time I looked, and I don't think there are lurking legacy 32-bit issues in that area that would bite us?

 -- Keir

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