How about that, in my previous patches, it actually allows three scenarios, 1) VRAM as display buffer 2) GTT as display buffer 3) Mixed GTT/display buffer, as you have asked. I think the first step is to make the 2nd scenario work at optimal level. After that, if anyone wants to work the 3rd scenario, I have no objection at all. Regards, Samuel Li > -----Original Message----- > From: Samuel Li [mailto:samuel.li at amd.com] > Sent: Wednesday, March 07, 2018 1:54 PM > To: Alex Deucher <alexdeucher at gmail.com> > Cc: Michel Dänzer <michel at daenzer.net>; Koenig, Christian > <Christian.Koenig at amd.com>; amd-gfx list <amd-gfx at lists.freedesktop.org> > Subject: Re: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support > > > You might also want to prefer VRAM, but also allow buffers to fall > > back to GTT if necessary. > For display buffer, this case seems not really attractive. When display buffer > changes between GTT and VRAM dynamically, our driver needs to adpat too, > which is hard to see the benefits and not really worth the effort. > > Sam > > > > On 2018-03-07 01:27 PM, Alex Deucher wrote: > > On Wed, Mar 7, 2018 at 1:18 PM, Samuel Li <samuel.li at amd.com> wrote: > >> I think it's not useful though. Think about that, SG display feature is > intended to use as less VRAM as possible. Will someone want a display > buffer sometimes VRAM, sometimes GTT? > >> Hardly a case to me, and I think it's a waste of effort. That also might > explain no driver does that now. > > > > You might want different strategies depending on how much VRAM you > > have. If you have a bunch and it performs better, prefer it. If you > > have limited VRAM, you might want to prefer GTT. You might also want > > to prefer VRAM, but also allow buffers to fall back to GTT if > > necessary. This would make the logic dynamic and all in one place. > > The kernel can advertise what asics support scanout from system ram > > and then UMDs can just query that to choose placements rather than > > adding hardcoded logic for specific asics. > > > > Alex > > > >> > >> Sam > >> > >> > >> > >> On 2018-03-07 12:50 PM, Michel Dänzer wrote: > >>> On 2018-03-07 06:38 PM, Alex Deucher wrote: > >>>> On Wed, Mar 7, 2018 at 12:29 PM, Samuel Li <samuel.li at amd.com> > wrote: > >>>>> > >>>>> Why so complicated? If old user space compatibility is required, just > use sg_display=0. > >>>> > >>>> It will always just work in that case and we can adjust for the > >>>> optimal scenario by default in all cases without requiring the user > >>>> to set misc parameters to tune their setup that may break in the > >>>> future or hide bugs because a user sets it and forgets it. > >>> > >>> Right. I don't agree it's all that complicated anyway, we do this > >>> sort of thing all the time, it also makes our lives easier down the road. > >>> > >>>
