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SubjectRe: [PATCH] i386 No Idle HZ aka dynticks 051221
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.

> More of an issue is that there are times when the laptop might think
> that it's running of the AC mains, but in fact the owner may have
> connected an external battery, and might _want_ the system to be as
> frugal as possible with the power.

Yes... OTOH it is not that bad -- we could simply hardcode data from
acpi BIOS into kernel, ignore what ACPI says, and drive C4 even on AC
power. But that would be hack (tm).

> Whether I boot from AC power battery seems to be immaterial; what
> seems to matter is whether or not the laptop is running on battery at
> the moment that /proc/acpi/processor/CPU0/power is sampled.

I did not realize ACPI was _that_ clever. Anyway, it is different on
my machine...
Thanks, Sharp!
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