Re: shrinking memory for suspend?

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Thursday, 3 May 2007 14:51, Paul Mackerras wrote:
> Rafael J. Wysocki writes:
> 
> > > Which is why the powermac/powerbook sleep code insists on there only
> > > being one cpu active.  I have an SMP powermac which can sleep; I use a
> > > little script to take the second cpu down before sleeping and bring it
> > > back up after waking up.
> > 
> > That's quite intrusive.  Ideally, user space processes should not notice that
> > there have been a suspend at one point.
> 
> Certainly, *most* userspace processes should not notice, and they
> don't.

This isn't quite true.  For example, if the suspend happens while one of the
'other' processes checks how many CPUs are online, it can get a wrong result
due to the suspend.

> But the process initiating the suspend most certainly knows 
> about the suspend happening.  And that's the one that arranges for
> taking the second cpu down and bringing it up.

Yes, obviously.

> So your objection seems silly to me, unless you meant something other than
> what your words seem to say.

Well, perhaps I should have used some other words, then. :-)

Besides, if your kernel is preemptible, the system behaves quite like an SMP
one.

Greetings,
Rafael