http://bugzilla.kernel.org/show_bug.cgi?id=6519
------- Additional Comments From [EMAIL PROTECTED] 2006-05-15 11:48 -------
On Mon, 15 May 2006, Andrew Morton wrote:
> > @@ -873,7 +866,8 @@ static int acpi_processor_get_power_info
> > for (i = 1; i < ACPI_PROCESSOR_MAX_POWER; i++) {
> > if (pr->power.states[i].valid) {
> > pr->power.count = i;
> > - pr->flags.power = 1;
> > + if (pr->power.states[i].type >= ACPI_STATE_C2)
> > + pr->flags.power = 1;
> > }
> > }
> >
> > --------8<--------
> >
> > The last change in the diff, in acpi_processor_get_power_info, is what
> > makes the
> > difference: commenting out the "if (pr->power.states[i].type >=
> > ACPI_STATE_C2)"
> > restores the power saving in 2.6.16.14 .
That last change is also the thing that fixed the lock-up for Maneesh.
We had this particular discussion at some point earlier, and didn't get to
any resolution. The ACPI people wanted to undo the thing, which didn't
make a lot of sense because (a) the comment says otherwise and (b) C1 is
available even without ACPI and (c) nobody ever explained why it locked up
without the "type >= ACPI_STATE_C2" test.
Now, what happens is that your ACPI tables show that C2+ is unusable,
which leaves only C1 usable (that, btw, you might be able to fix with
different tables - possibly through a BIOS update).
However, at that point it's totally pointless to even _try_ to use ACPI
CPU power management for this case, since ACPI can't do any better than
the normal C1 stuff in the bog-standard non-ACPI x86 idle routine.
Do you actally see anything running hotter?
Or is it just that the "CPU%d (power states:..)" message disappeared?
Please realize that we will _always_ use C1 (aka "halt") in the idle state
quite regardless of ACPI - unless you've done "idle=poll" on the kernel
command line. So the fact that we don't use ACPI for it shouldn't make us
actually run any hotter (quite the reverse - we'll go into C1 state with
_less_ work).
So I don't see the downside. Am I missing something?
Linus
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