Re: [TuxOnIce-devel] [RFC] TuxOnIce

[Nigel Cunningham <nigel@tuxonice.net>]

Hi.

On Thu, 2009-05-07 at 17:39 -0700, Jesse Barnes wrote:
> On Fri, 08 May 2009 10:13:38 +1000
> Nigel Cunningham <nigel@tuxonice.net> wrote:
> > 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.

It doesn't write directly to the framebuffer memory. It may (or may not)
have a userspace program running that uses the framebuffer to display
progress.

Regards,

Nigel