Re: suspend2 merge (was Re: [Suspend2-devel] Re: CFS and suspend2: hang in atomic copy)

From: Pavel Machek
Date: Wed Apr 25 2007 - 19:29:02 EST


> > > I don't understand how you can even *claim* something like that.
> >
> > BTW most problems are in thaw/resume functions.
> And do you realize that the thaw/resume functions are totally different
> too?
> Or rather, they *would* be, if you allowed them to.
> For example, for "snapshot + thaw", the _sane_ thing is to actually make
> the snapshot just throw away all the DMA tables etc, and let the thawing
> just do a full initialization (as it did on boot). It basically needs to
> do that anyway, and it simplifies the whole thing (ie you don't even
> *want* to save things like the DMA command queues etc - the ones that will
> quite often be stepped on by the final "write snapshot to disk" stuff
> anyway).

I'd prefer thaw to be similar to module insert, yes.

> For suspend to ram, in contrast, since you *know* that nobody will be
> touching the hardware, and since the timings are very different anyway
> (you'd hope that you can resume in a second or two), you'd generally want
> to keep the DMA engine tables right where they are, and just literally
> suspend the PCI chip itself.

I'd actually prefer resume to be similar to module insert, too... Do
you think that resume is _that_ time critical?

> You think they have things in common just because your whole (incorrect)
> mindset has _forced_ them to have things in common, becasue your setup
> stupidly thinks that "resume" is the same as "thaw", the same way you
> think "freeze" is the same as "suspend".
> NEITHER is true. You've _made_ them true in your mind, but there's
> absolutely zero reason that they *should* be true.

[I'd like you to drop me a line saying you understand current design
and that it works -- even if it is very inelegant]

Now, we can separate suspend/freeze and resume/thaw (with some common
helpers). It will speed the code up by avoiding unneccessary
operations. It also needs attetion from driver writers (ouch).

Do we want to do that?
(cesky, pictures)
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