On Tue, 18 Aug 2009 09:32:50 +0200 Thomas Hellström <tho...@shipmail.org> wrote:
> Jesse Barnes wrote: > > On Mon, 17 Aug 2009 22:22:34 +0200 > > Thomas Hellström <tho...@shipmail.org> wrote: > > > > > >> Kristian Høgsberg wrote: > >> > >>> This patch adds a vblank synced pageflip ioctl for to the > >>> modesetting family of ioctls. The ioctl takes a crtc and an fb > >>> and schedules a pageflip to the new fb at the next coming vertical > >>> blank event. This feature lets userspace implement tear-free > >>> updating of the screen contents with hw-guaranteed low latency > >>> page flipping. > >>> > >>> The ioctl is asynchronous in that it returns immediately and then > >>> later notifies the client by making an event available for reading > >>> on the drm fd. This lets applications add the drm fd to their main > >>> loop and handle other tasks while waiting for the flip to happen. > >>> The event includes the time of the flip, the frame counter and a > >>> 64 bit opaque token provided by user space in the ioctl. > >>> > >>> Based on work and suggestions from > >>> Jesse Barnes <jbar...@virtuousgeek.org>, > >>> Jakob Bornecrantz <wallbra...@gmail.com>, > >>> Chris Wilson <ch...@chris-wilson.co.uk> > >>> > >>> Signed-off-by: Kristian Høgsberg <k...@redhat.com> > >>> Signed-off-by: Jesse Barnes <jbar...@virtuousgeek.org> > >>> --- > >>> > >>> Ok, another version of this patch. This one has fixes to work > >>> with radeon kms plus a missing list head init that would cause an > >>> oops in the case where we schedule a flip before the previous one > >>> has been queued. > >>> > >>> I'm now ready to propose this patch for the 2.6.32 merge window. > >>> > >>> > >>> > >> Hi! > >> First a general question: There is some hardware (for example > >> Unichromes and Chrome9) that can schedule > >> page-flips in the command stream after optional vblank barriers. > >> For this kind of hardware the pageflip would be a matter of > >> scheduling the flip and fence the old and new buffers. No need > >> for delayed unpins and explicit user-space notifications, although > >> the workqueue could be handy to avoid command processing stalls in > >> the vblank barriers. How would such a scheme fit into the > >> framework below? > > > > If you fence the flip, doesn't that mean you only unpin after it's > > completed? The initial version of this patch used a command stream > > flip, but I still had to worry about pinning... > > > With a fenced flip (and some TTM terminology) it would amount to > > reserve(old_scanout); // Reserve means "claim buffer for > validation". reserve(new_scanout); > submit_flip(); > unpin(old_scanout); > pin(new_scanout); > fence(both_scanouts); > unreserve(old_scanout); > unreserve(new_scanout); > > So the pin / unpin would happen at command submission time and not at > flip execution time, > and the fence would make sure any old scanouts remain in GPU memory > until they are no longer referenced by the VDC. > > But the real benefit of this scheme is pageflipping without vblank > waits. I'm not sure the vblank barrier stalls are acceptable in > reality, since they block all command execution. Ah right, the fence semantics are a nice fit here. In this code we should only be blocking on rendering to the still active back buffer though; any other rendering will proceed normally (at least that was our intent). > > If you don't need the userspace notifications we could probably > > factor that out; do you see any issues with the flip ioctl itself? > > If not, we can change things as needed if/when more drivers support > > it... > > > > > No, I don't have anything against it at all. > I'm just trying to get a basic understanding how this would be > implemented with > different hardware, and as you say, we could change things if needed > if the need for it arises. Great, thanks a lot for looking at it. -- Jesse Barnes, Intel Open Source Technology Center ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
