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

[Bruce Cran]

On Thu, 26 Mar 2009 17:04:19 +0200
Andriy Gapon <avg at icyb.net.ua> wrote:

> on 26/03/2009 16:41 Bruce Cran said the following:

> > I added lots of printfs to acpi_cpu.c and found that it's occuring
> > in acpi_cpu_startup; initializing it to 3 in that function (which I
> > wrongly assumed was the lowest Cx state supported in ACPI) fixed
> > the problem on my Athlon XP PC because the generic cx handling code
> > then lowered cpu_cx_count to 1 based on the fact that
> > sc->cpu_cx_count was also 1.
> > 
> 
> Ok, yes, the real issue is in acpi_cpu_generic_cx_probe, namely in
> early exits from it. So,  sc->cpu_cx_count is always set to at least
> 1, but if we exit via one of the returns before the end of function,
> then global cpu_cx_count is never updated.
> 

Exactly:

acpi: acpi_cpu_startup: initializing cpu_cx_count to 0
acpi_cpu_generic_cx_probe
if sc->cpu_p_blk_len < 5  [sc->cpu_p_blk_len = 0]
acpi: acpi_cpu_startup: cpu 0,cpu_cx_count = 0,sc->cpu_cx_count = 1

So we're hitting an early exit in acpi_cpu_generic_cx_probe.

-- 
Bruce Cran