PATCH: Pentium-M deeper sleep support in idle loop

[Marko Zec]

Huh... the original version could result in occasional ata drive lockups. 
Hopefully improved version can be found on the same URL:

http://www.tel.fer.hr/zec/BSD/pm/4.8-ich-ds.patch

Marko

On Friday 17 October 2003 02:20, Marko Zec wrote:
> From http://www.tel.fer.hr/zec/BSD/pm/4.8-ich-ds.patch you can fetch an
> experimental patch for the 4.8-RELEASE kernel that allows for significant
> power savings on mobile systems by utilizing a feature called "deeper sleep
> mode". The deeper sleep mode is available on recent Intel mobile processors
> (Pentium III-M, Pentium IV-M and "Centrino" Mobile Pentium) in combination
> with ICH3 / ICH4 chipsets, and is used to simultaneously stop the CPU clock
> and significantly lower the chip core voltage. When in such a state, the
> CPU is supposed to consume only around 0.6 W, according to Intel specs.
>
> The power saving policy in idle loop is controlled by the
> machdep.cpu_idle_hlt sysctl, which now has two new modes:
>
> Mode 0  (std)  Do not halt the CPU, return from the idle loop as soon as
>                possible.
>
> Mode 1  (std)  Halt the CPU using the "hlt" instruction. CPU clock is not
>                stopped (TSC keeps counting).
>
> Mode 2  (new)  Halt the CPU using APM BIOS call followed by a "hlt". This
>                method stops the clock, thus saving slightly more power.
>
> Mode 3  (new)  Halt the CPU by entering the deeper sleep mode (max. power
>                savings).
>
> The battery life extension that can be obtained on an idle system using
> this patch looks very promissing. Here's what I could observe on my
> ThinkPad X30 (Pentium III-M 1200, ICH-3 chipset) with a slightly worn-out
> battery:
>
> +---------+----------------------+----------------------+
>
> |cpu_idle |      LCD ON (dim)    |        LCD OFF       |
> |  mode   | Bat. life |   gain   | Bat. life |   gain   |
>
> +---------+-----------+----------+-----------+----------+
>
> |    1    |    4:03   |          |    5:12   |          |
>
> +---------+-----------+----------+-----------+----------+
>
> |    2    |    4:10   |     2%   |    5:23   |     3%   |
>
> +---------+-----------+----------+-----------+----------+
>
> |    3    |    4:48   |    18%   |    6:21   |    22%   |
>
> +---------+-----------+----------+-----------+----------+
>
> I had no ICH-4 based laptop available for testing, so I cannot promise that
> the patch will work on such systems, although it should.
>
> The patch also introduces a new sysctl machdep.speedstep, which can be used
> to directly controll the CPU clock frequency / operating voltage. If your
> BIOS already correctly does this job you probably won't need this sysctl,
> however the BIOS in my ThinkPad annoyingly persists with the same speedstep
> mode regardless of the power source (external/battery), so I had to
> implement a method to control it.
>
> Anyhow, hope you like the patch... The usual liability disclaimer applies -
> if anything goes wrong with your machinery or data, you are on your own :-)
> Have fun,
>
> Marko