Re: [TuxOnIce-devel] [RFC] TuxOnIce

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Fri, 08 May 2009 10:13:38 +1000
Nigel Cunningham <nigel@tuxonice.net> wrote:

> Hi.
> 
> On Thu, 2009-05-07 at 16:43 -0700, Jesse Barnes wrote:
> > On Fri, 08 May 2009 09:32:34 +1000
> > Nigel Cunningham <nigel@tuxonice.net> wrote:
> > > On Thu, 2009-05-07 at 16:14 -0700, Jesse Barnes wrote:
> > > > On Fri, 08 May 2009 06:41:00 +1000
> > > > Nigel Cunningham <nigel@tuxonice.net> wrote:
> > > > 
> > > > > Hi.
> > > > > 
> > > > > On Thu, 2009-05-07 at 21:27 +0200, Rafael J. Wysocki wrote:
> > > > > > In fact I agree, but there's a catch.  The way in which
> > > > > > TuxOnIce operates LRU pages is based on some assumptions
> > > > > > that may or may not be satisfied in future, so if we decide
> > > > > > to merge it, then we'll have to make sure these assumptions
> > > > > > will be satisfied. That in turn is going to require quite
> > > > > > some discussion I guess.
> > > > > 
> > > > > Agreed. That's why I've got that GEMS patch - it's putting
> > > > > pages on the LRU that don't satisfy the former assumptions:
> > > > > they are used during hibernating and need to be atomically
> > > > > copied. If there are further developments in that area, I
> > > > > would hope we could just extend what's been done with GEMS.
> > > > 
> > > > Another option here would be to suspend all DRM operations
> > > > earlier. The suspend hook for i915 already does this, but maybe
> > > > it needs to happen sooner?  We'll probably want a generic DRM
> > > > suspend hook soon too (as the radeon memory manager lands) to
> > > > shut down GPU activity in the suspend and hibernate cases.
> > > > 
> > > > All that assumes I understand what's going on here though. :)
> > > > It appears you delay saving the GEM (just GEM by the way, for
> > > > Graphics/GPU Execution Manager) backing store until late to
> > > > avoid having the pages move around out from under you?
> > > 
> > > Yeah. TuxOnIce saves some pages without doing an atomic copy of
> > > them. Up 'til now, the algorithm has been LRU pages - pages used
> > > for TuxOnIce's userspace helpers. With GEM, we also need to make
> > > sure GEM pages are atomically copied and so also 'subtract' them
> > > from the list of pages that aren't atomically copied.
> > > 
> > > It's no great problem to do this, so I wouldn't ask you to change
> > > GEM to suspend DRM operations earlier. It's more important that
> > > GEM doesn't allocate extra pages unexpectedly - and I don't think
> > > that's likely anyway since we've switched away from X. This is
> > > important because TuxOnIce depends (for reliability) on having
> > > memory usage being predictable much more than swsusp and uswsusp
> > > do. (Larger images, less free RAM to begin with).
> > 
> > Yeah X is typically the one causing GEM allocations and performing
> > execution, but there are other possibilities too.  E.g. Wayland is a
> > non-X based display system that may be running instead, or maybe
> > there's an EGL or GPGPU program running in the background.
> > 
> > So I think it's best if we suspend DRM fairly early, otherwise you
> > *may* get extra allocations and will probably see all sorts of GPU
> > memory mapping activity and execution while you're trying to
> > hibernate things.  On the plus side I don't think this is a radical
> > redesign or anything, and mostly something we can do in our suspend
> > and hibernate callbacks.
> 
> That won't stop updates to the framebuffer?

No you can still have the framebuffer mapped and write to it (as long
as we don't invalidate such mappings at DRM suspend time that is, but
there's no reason to do that).

Does that mean tuxonice writes directly to framebuffer memory when
suspending?  Or does it just rely on a userspace program that does
that?  I'm just curious, either way should work fine, drm-wise.

Jesse