Re: Attempted summary of suspend-blockers LKML thread, take three

Paul E. McKenney
2010-08-15T07:00:04Z

On Sat, Aug 14, 2010 at 09:53:51AM -0700, Arjan van de Ven wrote:
> On Sat, 14 Aug 2010 08:10:48 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> >
> > So once you are down to one CPU, the last CPU shuts the system off,
> > itself included? Or does the last CPU "run" in a deep idle state
> > throughout suspend? (My guess is the former, and I am also curious
> > whether the cache SRAMs are powered off, etc. But figured I should
> > ask rather than guessing.)
>
> they tend to go "off".
>
> however I think you're making an assumption that there is a
> real difference between a deep idle state and "off"....
>
> For modern x86 hardware, that assumption isn't really valid.
> (other than a very very small sram that stores register content in the
> idle case)

I am and have been taking you at your word that some systems can reach
power levels while idle that rival suspended/off. The differences between
idle and suspend are instead semantic, have been posted here more than
once, and make themselves felt when the non-suspended system is non-idle,
even for systems whose deep-idle power approximates that of suspend/off.

Thanx, Paul