C4 strangeness [was Re: [PATCH] i386 No Idle HZ aka dynticks 051221]

C4 strangeness [was Re: [PATCH] i386 No Idle HZ aka dynticks 051221]

[Pavel Machek]

On Út 27-12-05 15:03:25, Pavel Machek wrote:
> On Út 27-12-05 00:27:12, Pavel Machek wrote:
> > On Po 26-12-05 17:52:48, Theodore Ts'o wrote:
> > > On Mon, Dec 26, 2005 at 09:38:06PM +0100, Pavel Machek wrote:
> > > > Stupid IBM. I've seen it appearing/disappearing, but did not work out
> > > > when.
> > > > 
> > > > No-C4-on-AC is bad -- if you just disconnect AC and walk away, you are
> > > > running without benefits of C4. Bad. Changing benchmarks depending on
> > > > you booting on AC or battery also look nasty.
> > > 
> > > The moment you disconnect AC, it C4 automagically appears.  When you
> > > reconnect to the AC mains, the C4 state disappears again, at least
> > > from the listing displayed by /proc/acpi/processor/CPU0/power.  So the
> > > first issue you brought up isn't a problem.
> > 
> > It does not seem to work like that here. I'm not sure what the exact
> > rules are, but I know that I sometimes have C4 and sometimes not. I
> > have C4 now, and it is used, even when I'm on AC power. Thinkpad
> > X32.
> 
> Well, today it _does_ behave like Theodore described (slightly
> different kernel, and I'm using power supply, not docking
> station). Strange.

So... I guess I found out what is going on.

When power is unplugged, X32 adds C4 state. When power is plugged, X32
removes C4 state (behaviour Ted seen). When I load ipw2200, this
behaviour stops, and I see everything up-to C4. Strange. I remember
ipw had some problems with C3 and C4, perhaps this is related?

								Pavel
-- 
Thanks, Sharp!

C4 non-strangeness [was: C4 strangeness [was Re: [PATCH] i386 No Idle HZ aka dynticks 051221]

[Dominik Brodowski]

Hi,

On Tue, Dec 27, 2005 at 03:22:38PM +0100, Pavel Machek wrote:
> So... I guess I found out what is going on.
> 
> When power is unplugged, X32 adds C4 state. When power is plugged, X32
> removes C4 state (behaviour Ted seen). When I load ipw2200, this
> behaviour stops, and I see everything up-to C4. Strange. I remember
> ipw had some problems with C3 and C4, perhaps this is related?

Nothing strange at all. The C-States are exported by the BIOS to the OS
using the _CST method/object/whatever. This can change on runtime. When the
BIOS recognizes it is on battery power, the _CST contains the C4 state, if
it is on AC power, the _CST doesn't contain it. The ACPI code follows what
it is told by the BIOS, for it has no chance to know about this additional
C-State if on AC power, and it wouldn't be wise to second-guess the BIOS.

Ipw does limit the max_cstate setting dynamically if it recognizes problems;
however I haven't seen _any_ such things lately on my own system. Might be
related to dyntick being _enabled_, though ;-)

	Dominik

Re: C4 non-strangeness [was: C4 strangeness [was Re: [PATCH] i386 No Idle HZ aka dynticks 051221]

[Pavel Machek]

On Út 27-12-05 16:33:30, Dominik Brodowski wrote:
> Hi,
> 
> On Tue, Dec 27, 2005 at 03:22:38PM +0100, Pavel Machek wrote:
> > So... I guess I found out what is going on.
> > 
> > When power is unplugged, X32 adds C4 state. When power is plugged, X32
> > removes C4 state (behaviour Ted seen). When I load ipw2200, this
> > behaviour stops, and I see everything up-to C4. Strange. I remember
> > ipw had some problems with C3 and C4, perhaps this is related?
> 
> Nothing strange at all. The C-States are exported by the BIOS to the OS
> using the _CST method/object/whatever. This can change on runtime. When the
> BIOS recognizes it is on battery power, the _CST contains the C4 state, if
> it is on AC power, the _CST doesn't contain it. The ACPI code follows what
> it is told by the BIOS, for it has no chance to know about this additional
> C-State if on AC power, and it wouldn't be wise to second-guess the BIOS.
> 
> Ipw does limit the max_cstate setting dynamically if it recognizes problems;
> however I haven't seen _any_ such things lately on my own system. Might be
> related to dyntick being _enabled_, though ;-)

This was without dynticks... But why C4 availability no longer changes
(between AC and battery power) with ipw2200 loaded? I'd understand
higher C states being unavailable...
								Pavel
-- 
Thanks, Sharp!