On Fri, May 22, 2020 at 6:41 AM Christian König <ckoenig.leichtzumerken@xxxxxxxxx> wrote: > > Am 20.05.20 um 18:18 schrieb Alex Deucher: > > On Wed, May 20, 2020 at 10:43 AM Christian König > > <ckoenig.leichtzumerken@xxxxxxxxx> wrote: > >> Am 13.05.20 um 13:03 schrieb Christian König: > >>> Unfortunately AGP is still to widely used as we could just drop support for using its GART. > >>> > >>> Not using the AGP GART also doesn't mean a loss in functionality since drivers will just fallback to the driver specific PCI GART. > >>> > >>> For now just deprecate the code and don't enable the AGP GART in TTM even when general AGP support is available. > >> So I've used an ancient system (32bit) to setup a test box for this. > >> > >> > >> The first GPU I could test is an RV280 (Radeon 9200 PRO) which is easily > >> 15 years old. > >> > >> What happens in AGP mode is that glxgears shows artifacts during > >> rendering on this system. > >> > >> In PCI mode those rendering artifacts are gone and glxgears seems to > >> draw everything correctly now. > >> > >> Performance is obviously not comparable, cause in AGP we don't render > >> all triangles correctly. > >> > >> > >> The second GPU I could test is an RV630 PRO (Radeon HD 2600 PRO AGP) > >> which is more than 10 years old. > >> > >> As far as I can tell this one works in both AGP and PCIe mode perfectly > >> fine. > >> > >> Since this is only a 32bit system I couldn't really test any OpenGL game > >> that well. > >> > >> But for glxgears switching from AGP to PCIe mode seems to result in a > >> roughly 5% performance drop. > >> > >> The surprising reason for this is not the better TLB performance, but > >> the lack of USWC support for the PCIe GART in radeon. > >> > >> > >> So if anybody wants to get his hands dirty and squeeze a bit more > >> performance out of the old hardware, porting USWC from amdgpu to radeon > >> shouldn't be to much of a problem. > > We do support USWC on radeon, although I think we had separate flags > > for cached and WC. That said we had a lot of problems with WC on 32 > > bit (see radeon_bo_create()). The other problem is that, at least on > > the really old radeons, the PCI gart didn't support snooped and > > unsnooped. It was always snooped. It wasn't until pcie that the gart > > hw got support for both. For AGP, the expectation was that AGP > > provided the uncached memory. > > Oh, indeed. I didn't remembered that. > > Interesting is that in this case I have no idea where the performance > difference is coming from. > > > > >> > >> Summing it up I'm still leaning towards disabling AGP completely by > >> default for radeon and deprecate it in TTM as well. > >> > >> Thoughts? Especially Alex what do you think. > > Works for me. > > I will take that as an rb and commit at least the first patch. Yeah, Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx> > > Thanks, > Christian. > > > > > Alex > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
