Re: Power consumption HZ100, HZ250, HZ1000: new numbers

[Ondrej Zary <linux@rainbow-software.org>]

James Bruce wrote:
> Ondrej Zary wrote:
>
> > James Bruce wrote:
> >
> > > Stephen Clark wrote:
> > >
> > > > Maybe new desktop systems - but what about the tens of millions of 
> > > > old systems that don't.
> > >
> > >
> > > If it's an old system, it probably doesn't have working ACPI C-states 
> > > though.  Without that, low HZ does not save you anything.  I should 
> > > have said: 99% of desktops with the capability to do ACPI sleep have 
> > > at least one USB device attached (usually a mouse).
> >
> >
> > rainbow@pentium:~$ cat /proc/acpi/processor/CPU0/power
> > active state:            C2
> > max_cstate:              C8
> > bus master activity:     00000000
> > states:
> >     C1:                  type[C1] promotion[C2] demotion[--] 
> > latency[000] usage[00052470]
> >    *C2:                  type[C2] promotion[--] demotion[C1] 
> > latency[090] usage[02699149]
> >
> > This is PCPartner TXB820DS motherboard (Socket 7, i430TX) with 1998 
> > Award BIOS and C-states seem to work fine. I've tested it in Windows 
> > 98 some time ago - the CPU is almost cold when idle with ACPI enabled 
> > and hot with ACPI disabled (that's partly caused by the fact that 
> > Windows 9x does not HLT the CPU when idle). With Pentium 100MHz in the 
> > socket and ACPI enabled, I could even touch the CPU (without heatsink) 
> > without burning my fingers.
>
>
> Ok I stand corrected, I had no idea there were machines that old where 
> ACPI worked correctly in Linux.
>
> Do you see the same kind of heat reduction in Linux as Win98?  What HZ 
> value are you using, as the latency for entering C2 on your machine 
> looks pretty substantial (Your C2 almost looks like a new machine's C3 
> state, which is supposedly the first level where substantial power 
> savings occur on a new machines).
I did some tests:
1. disconnected CPU fan power
2. booted 2.6.12 (compiled with HZ=100) with init=/bin/sh
3. left it idling on the shell prompt and checked CPU heatsink 
temperature (by hand) - only warm
4. rebooted the same kernel with acpi=off init=/bin/sh
5. left it idling on the shell prompt and checked CPU heatsink 
temperature - warm and slowly getting hot
6. rebooted the same kernel with init=/bin/sh again
7. left it idling on the shell prompt and checked CPU heatsink 
temperature - temperature went back to "warm" :)

Result: ACPI C2 state reduces CPU consumption here
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