[coreboot] Lenovo X200 running Coreboot drains 3-4W more power than with Vendor BIOS

[Nico Huber]

On 01.05.2016 21:40, Daniel Kulesz wrote:
> Hi again,
> 
> I did some more experiments with the vendor BIOS and made the following
> observations:
> 
> - disabling "cpu power management" makes the idle consumption raise to 12,8W
Is this 12.8W compared to 7.5W (i.e. with lowest backlight)?

> - disabling "PCI Bus power management" and "PCI express power management" makes the idle consumption raise to 13,3W
> - disabling the AMT firmware had no effect
> - running the stress test still drains only 24,2W
> - performance is the same as before
>
> I still don't understand the whole performance issue. Therefore, I took
> another X200 with a P8600, CCFL screen and an older vendor BIOS and
> re-ran the benchmark there --- with almost identical results.
> 
> So in the end I'm just confused. This would mean that running Coreboot
> makes the X200 *much* faster at the expense of battery life, both in
> idle and under stress conditions.
> 
Maybe Lenovo limited the processor clock on purpose to get a better
battery life. Maybe it's just an unexpected side effect of running
Linux (not Windows, what Lenovo tested against). Anyway, I wouldn't care
about the power consumption under load, it might even result in a longer
battery life: Being faster means shorter periods in higher performance
states. The idle power consumption is what really matters.

> Any ideas which could solve this mystery?
>
One more thing you can test, in case your Linux uses the intel_idle
driver: There is a kernel parameter intel_idle.max_cstate, if you boot
the vendor BIOS with defaults and Linux with
  intel_idle.max_cstate=2
it should use C1/C2 but not C3/C4 and thus behave more like coreboot.

Nico