Hi, i own a Thinkpad X60s, same chipset, and setting/unsetting the bit doesn't change my powerusage a bit (normally just aroung 10W), tested with kernel 2.6.21 ..
On Thu, 21 Jun 2007, Török Edvin wrote: > My system reports C3 as deepest sleep-state. Arjan once said on this > ML that the BIOS should remap C3 to C4. I made some experiments to > find out if my BIOS really did that or not. > > I have an ICH7-M (82801GBM) motherboard, downloaded the datasheet for > it (30701303.pdf), and on page 419 I see there is a bit C4onC3_EN in > GEN_PMCON_1 register, that does the remapping Arjan talked about. > Using lspci -xxx -s 00:1f.0 I found out that it was disabled (and so > was Intel SpeedStep)! > > So I did the following experiment (without the AHCI ALPM enabled): > Power consumption in default state : ~12 W > Turn on C4onC3_EN, and speedstep: setpci -s 00:1f.0 a0.w=a8 > Power consumption after >30s: 10.5W (1.5W savings!) > Turn off C4onC3_En: setpci -s 00:1f.0 a0.w=20 > Within seconds power consumption rises to 12 W > > [If somebody else wants to try this, make sure you read your chipset's > datasheet first!] > > Clearly this is something thats worth enabled, and I wonder why the > BIOS doesn't enable it. > Reading through the datasheet, I find that there is a P_LVL4 register > that when read will make CPU enter C4 state. (page 439, LV4 register). > Its address can be find out from ACPI P_BLK+6. > > I see that Linux only support up to ACPI C3 (P_LVL3: P_BLK+5). A quick > glance at the ACPI spec tells me there is no ACPI C4. Is this LV4 > register on ICH7-M non-standard? > Would it be worth adding support for ACPI C4 (P_BLK+6) for > motherboards that support it , even if the BIOS won't report it in its > _CST tables? [My _CST table containts 3 C states for CPU0, and 1 > C-state for CPU1). > > BTW, Intel docs say CPU C4 state (which is not the same as ACPI > C-states?) is same as C3, unless _both_ cores enter C4, then the > package-level low-power mode will be activated. Maybe it would be > useful for powertop to show C-state usage for _both_ cores (i.e. if > they both entered C3/C4 or not)? > > There are also extended C-states (C1E, C2E,...C4E) usable via MWAIT > eax hints register, but docs say the BIOS should activate these, but > it obviously doesn't (I don't even have C4, let alone C4E). Should I > venture in trying to use C4E, or will that void my warranty or > something like that? -- Florian Reitmeir _______________________________________________ Power mailing list [email protected] http://www.bughost.org/mailman/listinfo/power
