STI, HLT in acpi_cpu_idle_c1

Don Bowman don at
Thu Jun 17 23:59:12 GMT 2004

From: Matthew Dillon [mailto:dillon at]
>     Probably not P72.. that would result in weird, inconsistent panics
>     rather then consistent hangs.  To make sure, just cool 
> your cpu down
>     a little (open the case and point a big fan at it).  If nothing
>     changes then it isn't P72.

Its definitely not hot, plenty of blowers, in an air-conditioned
room, has been qualified in environmental chamber.

>     The STI; HLT sequence is definitely working properly... operating 
>     systems have depended on that code sequence forever.  Going down
>     that path is a red herring.
>     If NMI can't stop the other processors w/ IPI STOP then 
> the PC for those
>     cpus that you see in the dump is not necessarily going to be where
>     they are actually hung.

Its not that they're hung, the emulator allows me to see
the current PC, registers, etc. They really are sitting
with interrupts locked off. In the case that i modified
the db to time out on the stop ipi, i can believe that the
stacks weren't necessarily consistent, although they seemed
to be. In the case I'm using the emulator it seems correct.

>     It kinda sounds like ACPI has bokered the other cpus.  
> I'm not sure
>     why one would even *want* to use ACPI to idle down Xeon's in an MP
>     system, actually :-)

Its not so much that I want to use ACPI, its 
that the machine doesn't boot without it, and it
can't be disabled later. You do want the HLT on idle,
like the sysctl enabled on releng_4, otherwise the performance
goes down and the power goes up.

I will keep digging, thanks muchly for the input. The
other option i will pursue is whether the APIC structure
has been altered somehow, something changed in there, etc.


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