Messages in this thread | | | Date | Wed, 16 Apr 2008 14:22:38 -0500 | From | Jack Steiner <> | Subject | Re: [PATCH] - Increase MAX_APICS for large configs |
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On Wed, Apr 16, 2008 at 08:45:43PM +0200, Ingo Molnar wrote: > > * Jack Steiner <steiner@sgi.com> wrote: > > > Increase the maximum number of apics when running very large > > configurations. This patch has no affect on most systems. > > > > Signed-off-by: Jack Steiner <steiner@sgi.com> > > > > I think this area of the code will be substantially changed when the > > full x2apic patch is available. In the meantime, this seems like an > > acceptible alternative. The patch has no effect on any 32-bit kernel. > > It adds ~4k to the size of 64-bit kernels but only if NR_CPUS > 255. > > ugly ... but well - applied. What's the static size cost of 64K APICs?
64k APICs would add ~8k to the static size of the kernel. Most of the increase is in the phys_cpu_present_map[].
When the x2apic patch is integrated, I expect (may be wrong) that this array will be eliminated since x2apic increases the max APIC_ID to 32 bits,
Note that MAX_APICS is really misnamed. It is not the maximum number of APICs. It is the value of the largest APIC ID. IDs are not necessarily dense.
--- jack
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