* David Rientjes <[email protected]> wrote:
> On Sat, 25 Jan 2014, Dave Jones wrote:
>
> > > > it looks like this is because..
> > > >
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled)
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x02] lapic_id[0x02] enabled)
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x03] lapic_id[0x04] enabled)
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x04] lapic_id[0x06] enabled)
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x05] lapic_id[0xff] disabled)
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x06] lapic_id[0xff] disabled)
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x07] lapic_id[0xff] disabled)
> > > > [ 0.000000] ACPI: LAPIC (acpi_id[0x08] lapic_id[0xff] disabled)
> > > >
> > > > Should the CPU counting code be ignoring those disabled APICs ?
> > >
> > > Hm, so to the kernel it looks like as if those were 'possible CPUs',
> > > in theory hotpluggable. Not sure what they are - disabled cores in an
> > > 8-core system? Or BIOS reporting crap?
> > >
> > > But perhaps the boot message could be improved to say something like:
> > >
> > > > [ 0.000000] smpboot: 8 possible processors exceeds NR_CPUS limit of
> > 4
> >
> > It's not possible though. It's an i5-4670T, in a single socket board.
> > It doesn't even have hyperthreading.
> > http://ark.intel.com/products/75050/Intel-Core-i5-4670T-Processor-6M-Cache-up-to-3_30-GHz
> >
>
> I don't think the "ACPI: LAPIC (... disabled)" lines are problematic, they
> are simply reporting the acpi processor id and apic id for processors that
> do not have their enabled flag set. The acpi spec allows for these to
> exist without the enabled flag set when the processor isn't present at all
> because the kernel will make no attempt to use it.
>
> That said, I think the "smpboot: 8 Processors exceeds NR_CPUS limit
> of 4" line is unnecessary since, as you said, these processors don't
> physically exist. I betcha that's because you have
> CONFIG_HOTPLUG_CPU enabled and it's counting the disabled cpus that
> were found when acpi_register_lapic() was done. The warning is only
> really meaningful for cpus in cpu_possible_map, which aren't set for
> your disabled four, in the hotplug case where NR_CPUS is too small.
No, this message is printed in prefill_possible_map() which
_generates_ cpu_possible_map, so '8' is the number of bits in
cpu_possible_map.
So the problem is that the counting of disabled but hotpluggable CPUs
is over-eager. Since I haven't actually seen _true_ hotplug CPU
hardware yet, I'd argue we do the change below - allocating space for
never-present CPUs is stupid. If there's true hot-plug CPUs around
that could come online after we've booted, then we want to know about
them explicitly.
Thoughts?
Thanks,
Ingo
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index a32da80..75a351a 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1223,10 +1223,7 @@ __init void prefill_possible_map(void)
i = setup_max_cpus ?: 1;
if (setup_possible_cpus == -1) {
possible = num_processors;
-#ifdef CONFIG_HOTPLUG_CPU
- if (setup_max_cpus)
- possible += disabled_cpus;
-#else
+#ifndef CONFIG_HOTPLUG_CPU
if (possible > i)
possible = i;
#endif
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