On Thu, Nov 26, 2015 at 10:30:57AM +0000, Chris Wilson wrote: > On Thu, Nov 26, 2015 at 10:34:51AM +0100, Daniel Vetter wrote: > > On Wed, Nov 25, 2015 at 09:58:28AM +0000, Chris Wilson wrote: > > > One thing I did notice when also dealing with memory > > > pressure flushing backbuffers was (a) they were unaligned and so needed > > > rebinding before pinning > > > http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=nightly&id=df636036d120c6227d1918cfd6d70232d8d37b4c > > > > Not sure I read this correctly, but shouldn't we cache the alignment for > > as long as the buffer isn't purged? Your patch resets when we unpin the > > last display user. So in your scenario above that could result in an > > unaligned rebinding for GT first, then aligned rebinding for display. I > > figured the idea is to get things right for the render right away? > > It was focused on the solving the problem that scanout needed to realign > the buffer. I felt that keeping the maximum alignment imposed by the > user was just asking for trouble. (It's actually a bug in that patch > that the alignment is reset there, it should be when > framebuffer_references drops to zero. Also note that is depends upon the > vma being persistent until closed.) > > > Only risk is that we might overalign things, but that only happens when > > userspace reuses fbs and non-fbs in a mixed fashion. But that shouldn't be > > a real problem I think. > > Probably not, just I don't trust them! The goal is keep the maximum > restriction for only as long as it makes sense. We want relaxed fenced > layout (because space is at a scarce resource on that hw), so always > binding a tiled object at its max alignment is counter productive. > framebuffers are typically only created for as long as required (give or > take a small amount of caching, either in the flip-sequence or by a > timer on idle). So keeping the fb's vma aligned seems a worthwhile > tradeoff to avoid having to rebind it just as we want to present it to > the screen. We have no time bounds on the user alignment, so that will > seem to be always at odds with reducing the alignment for improved packing > at the earliest opportunity. > > I'm pretty certain that fb alignment is the only restriction we wish to > keep. Yeah, keeping fb alignment until fb_refs drops to 0 makes sense. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
