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SubjectRe: [linux-usb] power management (WAS Re: [linux-usb] OHCI crash)
On Wed, Mar 22, 2000, Jamie Lokier <lu@tantalophile.demon.co.uk> wrote:

>That depends what kind of suspend. If I shut the lid of my laptop, I do
>_not_ want it to spend 5 seconds swapping before it can save the 4MB of
>video state. That's what suspend-to-disk is for. But when I shut the
>lid, I want sleep , which means there's enough power to retain the
>memory (including VRAM) but devices like USB controllers are powered

Well, then that would be "sleep levels". Note that with our current code
on powerbook, it usually sleeps after one or two seconds and rarely have
to swap. Some video chipsets can go to suspend mode _and_ retain the VRAM
content. That's really a matter of how much power you want to save.

Something, for example, MacOS does very well is monitoring machine
activity and suspending selected devices or putting the CPU in a slower
mode when activity is low. On PPC, we can DOZE the CPU in the idle task,
but we lack more extensive monitoring that would allow us to turn off the
L2 cache for exampe when overall CPU activity remains low and stable.
Also, USB can be suspended more often in some cases, brightness can be
lowered too when machine is idle, etc..

Of course all these need to be turned on/off depending on the user's
preferences and what the machine is used for.




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