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

Ondrej Zary
2005-08-11T19:22:12Z

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