Messages in this thread | | | Date | Thu, 26 Apr 2007 02:14:14 +0200 | From | Pavel Machek <> | Subject | Re: suspend2 merge (was Re: [Suspend2-devel] Re: CFS and suspend2: hang in atomic copy) |
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Hi!
> > > Why? Becuase there is no _room_ for inconsistency. There's nothing to be > > > "inconsistent with", since any changes to memory (by things like DMA or > > > other setup that happens while the suspend process is going on) is by > > > _definition_ consistent with the resume image (becasue there is no > > > separate image). > > > > Do you propose to keep DMAs running while suspending-to-RAM? > > What part of "suspend a chip" do you have trouble with? > > DMA obviously does *not* happen with a suspended device. There's no need > to turn DMA even off - it just doesn't happen!
Ok, I guess I'll have nightmares of DMA controllers doing DMAs from chips that are no longer there tonight.
> > > For example, the whole myth that "freeze" needs to shut off DMA is a total > > > and utter *myth*. It needs nothing of the sort at all. Rather than shut > > > off DMA and try to make the hardware be wevy wevy quiet while it's hunting > > > wabbits, it's a lot easier to just do nothing at all on "freeze", > > > > No. Sorry, you are wrong here. > > > > Remember that during resume we run > > > > freeze() > > copy old data into memory > > thaw() > > > > Now, if the old kernel left DMAs running, it could be overwriting > > the data we are copying in. > > The *thaw* needs to happen with devices quiescent. > > But that sure doesn't have anythign to do with the "snapshot()" path. In > fact, you'll have rebooted the machine in between.
Only the fact that we are currently using same device call during snapshot() and during restore(). We obviously could do _5_ device calls
(suspend/resume/freeze/quiesce_disable_dma/thaw)
...but that looks like too many calls to me.
> So what does that have to do with "snapshotting"?
I'm not comfortable with memory I'm copying changing under my hands because of some DMA. It just looks like asking for trouble. I _think_ we can get away with DMA running during snapshot, because driver may not assume anything about the DMA result before it got completion interrupt, but...
Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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