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SubjectRe: Which is simpler? (Was Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.)
Date
Hi.

On Monday 20 February 2006 10:53, Pavel Machek wrote:
> Hi!
>
> > > > It is a lot slower because it does all it's I/O synchronously,
> > > > doesn't compress the image and throws away memory until at least half
> > > > is free.
> > >
> > > uswsusp does compress image (20% speedup, in recent CVS) and do
> > > asynchronous I/O.
> >
> > Only 20? You must be doing something horribly wrong. Asynchronous
>
> 20% is speedup for compression alone, over whole suspend
> process. Device suspend/resume takes lot of time in recent kernels.

Ok. I'm not counting device suspend/resume time, but if you do, the percentage
will vary according to the image size (since the device suspend/resume time
should be independant of image size).

> > > > > > The only con I see is the complexity of the code, but then again,
> > > > > > Nigel
> > > > >
> > > > > ..but thats a big con.
> > > >
> > > > It's fud. Hopefully as I post more suspend2 patches to LKML, people
> > > > will see that Suspend2 is simpler than what you are planning.
> > >
> > > For what I'm planning, all the neccessary patches are already in -mm
> > > tree. And they are *really* simple. If you can get suspend2 to 1000
> > > lines of code (like Rafael did with uswsusp), we can have something to
> > > talk about.
> >
> > Turn it round the right way. If you can get the functionality of Suspend2
> > using userspace only, then we have something to talk about.
>
> Only feature I can't do is "save whole pagecache"... and 14000 lines
> of code for _that_ is a bit too much. I could probably patch my kernel
> to dump pagecache to userspace, but I do not think it is worth the
> effort.

Yes, 14,000 lines for that alone would be a bit too much :)

> > > > Let's be clear. uswsusp is not really moving suspend-to-disk to
> > > > userspace. What it is doing is leaving everything but some code for
> > > > writing the image in kernel space, and implementing ioctls to give a
> > > > userspace program the ability to request that other processes be
> > > > frozen, the snapshot prepared and so on. Pages in the snapshot are
> > > > copied to userspace, possibly compressed or encrypted there in
> > > > future, then fed back to kernel space so it can use the swap routines
> > > > to do the writing. Very little of substance is being done in
> > > > userspace. In short, all it's doing is adding the complexity of
> > >
> > > Maybe very little of substance is being done in userspace, but all the
> > > uglyness can stay there. I no longer need LZF in kernel, special
> > > netlink API for progress bar (progress bar naturally lives in
> > > userland), no plugin infrastructure needed, etc.
> >
> > And you do need?...
>
> I do not need anything more than what is already in -mm tree.

You misunderstand me. Let me reprhase. What additional dependencies do you
have in userspace to support this? libabc, v >= x.y.z etc.

> > > If you can do suspend2 without putting stuff listed above into kernel,
> > > and in acceptable ammount of code... we can see. But you should really
> > > put suspend2 code into userspace, and be done with that. Feel free to
> > > spam l-k a bit more, but using existing infrastructure in -mm is right
> > > way to go, and it is easier, too.
> >
> > It is only easier because you're not comparing apples with apples. I have
> > no desire to spam LKML with this pointless discussion, so I'm just going
> > to get on with submitting patches for review.
>
> So please take my comments from "suspend2 review" mail into account.

Am going, as I do with all responses. Please just remember that taking them
into account doesn't equate to slavishly doing everything suggested.

Regards,

Nigel

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