Hi, 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? Best regards, Edwin _______________________________________________ Power mailing list [email protected] http://www.bughost.org/mailman/listinfo/power
