kern/108581: [sysctl] sysctl: hw.acpi.cpu.cx_lowest: Invalid argument

[Stephane E. Potvin]

John Baldwin wrote:
> On Thursday 26 March 2009 10:37:31 am Bruce Cran wrote:
>> On Thu, 26 Mar 2009 09:37:50 -0400
>> John Baldwin <jhb at freebsd.org> wrote:
>>
>>> No, the code is doing things differently on purpose (though I'm not
>>> completely sure why).  For _CST it sets cpu_cx_count to the maximum
>>> Cx level supported by any CPU in the system.  For non-_CST it sets it
>>> to the maximum Cx level supported by all CPUs in the system.  I think
>>> it is correct for cpu_cx_count to always start at 0 and only be
>>> bumped up to a higher setting.  Setting it to 3 would be very wrong
>>> for the _CST case as I've seen CPUs that support C4.
>> From briefly reading through the specifications I'd assumed the maximum
>> power state was C3.
> 
> For the non _CST case that is all that is defined, yes.  However, _CST is a 
> variable length array of Cx states, so it can support arbitrary numbers of 
> states.
> 
>> I had thought the _CST block was wrong because in
>> acpi_cpu_global_cx_lowest_sysctl it validates the new value against
>> cpu_cx_count; if one CPU has a lower cx state than the others, then
>> won't this tell the other CPUs to use an unsupported state?
> 
> It depends on if the CPU driver is smart enough to cap requests to 
> sc->cpu_cx_count, though if it does presumably it would do that in the 
> cx_generic case as well.  I'm not sure why it behaves differently for the 
> _CST case, but I do think it is on purpose at least rather than an accidental 
> bug.  Perhaps Nate can chime in with why?
> 

The intent when I added support for cx states on SMP systems was to use
the same maximum cx_state for all CPUs when _CST is not used (cx_generic
case) and to respect per-processor maximum cx_state when _CST is present
and can be used. This whole piece of code is really convoluted and
there's been a few errors found in it over time so I wouldn't be
surprised if there were some still lurking.

Could you send me privately a copy of your ASL and a verbose boot log?

Steph