RE: [PATCH v6 04/12] x86/smpboot.c: Don't offline CPU0 if any irqcan not be migrated out of it and remove CPU0 check in smp_callin()

[Yu, Fenghua]

> From: Luck, Tony
> Sent: Monday, May 14, 2012 9:41 AM
> To: Ingo Molnar
> Cc: Thomas Gleixner; Yu, Fenghua; Ingo Molnar; H Peter Anvin; Linus
> Torvalds; Andrew Morton; Mallick, Asit K; Arjan Dan De Ven; Siddha,
> Suresh B; Brown, Len; Srivatssa S. Bhat; Randy Dunlap; Chen Gong;
> linux-kernel; linux-pm; x86; Peter Zijlstra
> Subject: RE: [PATCH v6 04/12] x86/smpboot.c: Don't offline CPU0 if any
> irq can not be migrated out of it and remove CPU0 check in smp_callin()
> 
> > Could we just standardize on NMI bringup during regular bootup?
> 
> I don't know for sure (Fenghua?) but I'd guess not. CPU#0 is being
> brought *back* online
> by this NMI ... i.e. it has been online before, so interrupt vector
> tables and CR3
> etc. have been set to Linux-y values. When bringing other cpus online
> for the first
> time they have nothing set so we'd still have to use INIT.

Yes, on platforms of apic_physflat, apic_flat, x2apicapic, etc, the INIT sequence is necessary for bringing up AP's because AP's are in BIOS initialized unknown status without interrupt tables and CR3 etc.

Thanks.

-Fenghua
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