power management, ahci link power management and DragonFly

Alex Hornung ahornung at gmail.com
Mon Nov 8 10:29:06 PST 2010

On 08/11/2010 15:16, Johannes Hofmann wrote:
I didn't see those on my thinkpad when adding link power management.
It looks like a bug. Are you getting those for each request, or just
when activating it?
What exact type of thinkpad and harddrive do you use?
My ThinkPad is a T60 8744-HDG with a Hitachi HTS541616J9SA00 drive. And 
it happens for any request, I think. Or maybe for the first one every 
short while.

I played around with it a bit and to me it seemed that wakeups are not
that much of a big deal. E.g. decreasing HZ (just for testing) didn't
gain much. But I might be missing something as everyone in Linux-land
talks about reducing the wakups and tickless kernels.
Well, I really don't know why we are so power inefficient. Our frequency 
is already rather low at 100 Hz, but something is going on that isn't 
quite right.


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