AHCI aggressive powersaving

[John Fremlin]

Kristen Carlson Accardi <kristen.c.accardi at intel.com> writes:
[...]
> I've updated the hardware based patches and posted to the mailing list - 
> they do indeed save anywhere from .6-1.5 watts depending on the system,
> on my X60 they save about a watt.  I don't think that a hardware based
> solution is irrelevant at all - it will usually be able to make faster
> and more accurrate decisions about when to place the link into lower
> power state than software could.

Fair enough. But could I point out that the patch I posted from Tejun
Heo actually does "stop" the port, not just putting it into low power
slumber modes.

So, I think it might be able to save more power.

Please take a look at it. It is quite sophisticated and could be
generalised to more chipsets. Perhaps, on AHCI it can be used in
combination with the aggressive link power management.

> Note that the previous implementation that was posted didn't work for me,
> so I just redid everything.

Was that my implementation? 

I posted it in November last year. It certainly isn't as good as yours

http://marc.info/?l=linux-kernel&m=116343039621877&w=2

As you can see, I too thought it saved about 1 W, but Pavel Machek
measured 250mW.