Re: [RFD] CPU hotplug and suspend

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > > Currently, we use the CPU hotplug to disable nonboot CPUs in the suspend code
> > > paths, but with the recent change of code ordering (ie. nonboot CPUs are
> > > disabled after freezing tasks _and_ devices) it has become quite troublesome.
> > > The reason of this is that there are some CPU hotplug notifiers registered and
> > > called on each run of cpu_up()/cpu_down() that assume the system to be fully
> > > functional, which is not the case during the suspend.  Moreover, at least some
> > > of them do things that are not really necessary for disabling or enabling the
> > > nonboot CPUs.
> > 
> > Right.
> > 
> > > The advantage of using the CPU hotplug (in its current form) for suspending is
> > > that if some CPUs don't reappear during the resume, we are safe.  Still, I
> > > think it would be more appropriate, and simpler in the long run, to notify the
> > > interested subsystems _only_ if one (or more) CPUs are not functional after the
> > > resume. 
> > 
> > I'm afraid that adding 'cpu not there so simulate unplug' path will
> > make it complex, and prone to failure, as _noone_ is going to test it.
> 
> Does it mean you think we should stick with the current approach and sort out
> all issues as they show up, or should we go for not using the CPU hotplug for
> suspending without implementing the 'cpu not there so simulate unplug' path
> at all (eg. we can fail the resume instead)?

I'd fix the current approach, but...
									Pavel
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